CN101176297B - Multi-channel transmission of quantum information - Google Patents
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Abstract
A communication system adapted to use wavelength (frequency) division multiplexing for quantum-key distribution (QKD) and having a transmitter coupled to a receiver via a transmission link. In one embodiment, the receiver is adapted to (i) phase- shift a local oscillator (LO) signal generated at the receiver, (ii) combine the LO signal with a quantum-information (QI) signal received via the transmission link from the transmitter to produce interference signals, (iii) measure an intensity difference for these interference signals, and (iv) phase-lock the LO signal to the QI signal based on the measurement result, hi one configuration, the QI signal has a plurality of pilot frequency components, each carrying a training signal, and a plurality of QKD frequency components, each carrying quantum key data. Advantageously, the system can maintain a phase lock for the QKD frequency components of the QI and LO signals, while the QKD frequency components of the QI signal continuously carry quantum key data.
Description
The cross reference of related application
The application requires the U.S. Provisional Patent Application No.60/681 that the title of submission on May 17th, 2005 is " Auantum Keydistribution ", 726 priority.The U.S. Patent application No.xx/xxx that it is " Multi-ChannelTransmission of Quantum Information " that the theme of this application relates to the title of the application's phase same date submission, the theme of xxx, it is incorporated by reference in this text examines.
Technical field
The present invention relates to optical communication equipment, more specifically, relate to the equipment for using quantum cryptography transmitting encrypted data.
Background technology
Conventionally the art that accesses to your password with the confidentiality that strengthens or even perfectly confidentiality between two or more nodes (user, stand), exchange messages.Typical encryption method is used avowed encryption/decryption algorithm, and the confidentiality of transmitted information is provided by the privacy key using in conjunction with this algorithm.Conventionally, privacy key is random selection, sufficiently long bit sequence.For example, in symmetric encryption scheme, dispatching station uses secret key encryption information and enciphered data is sent on common signal channel to receiving station.Receiving station is used subsequently same key to decipher this encryption and recovers raw information.
The longer system of key is safer, and this is well-known.For example, a kind of widely used encryption system-data encryption standard (DES) has the key length of 56 bits.Except attempting 2
56plant possibility key value to crack outside DES, there is no more efficiently method.But, if listener-in has powerful computing capability, still can crack DES.Therefore,, in order to realize higher fail safe, can use single sheet (one-time pad) (with the same key of growing of transmission message).Be safe although use the communication system of single sheet in theory with respect to the attack based on absolute computing capability, so a kind of system must be processed so-called encryption key distribution problem, safely key is offered to the problem at sending/receiving station.
Use conventional (typically) cipher key transmission methods, the stolen hearer's PASSIVE SURVEILLANCE of its possibility, the certifiable privacy key of more difficult transmission, and the common physical security measures that needs trouble.But, use quantum technology can realize privacy key and distribute.More specifically, in quantum cryptography, send privacy key by specified quantitative subchannel, the fail safe of described quantum channel is based on principle of quantum mechanics.More specifically, the quantum state of system is inevitably revised in any measurement of the quantized system of suitably selecting, and this is well-known.Therefore, in the time that listener-in attempts to measure from quantum channel obtaining information by execution, validated user can detect the fact of having carried out measurement, and therefore it will abandon all safe keys that jeopardize.
In fact, can use following method to set up quantum channel, for example (i) is by the single photon sequence of spread fiber, with the polarization of photon or the key bit of phase code, or (ii) train of coherent optical pulses, comprise respectively a small amount of (for example, lower than hundreds of) photon, use the quadrature value coded key bit of the selected variable that characterizes each pulse.The more details that can find to set up and use typical amount subchannel in the comment that the title of disclosed the 74th volume 145-195 page N.Gisin, G.Ribordy, W.Tittel and H.Zbinden is " Quantum Cryptography " in Reviews ofModern Physics in 2002, its instruction is incorporated herein by reference.
Although make certain gains for the equipment of quantum channel in exploitation, this equipment does not still reach performance objective, for example, in quantum-key distribution (QKD) speed and transmission range.For example, the current approximately QKD speed of 1.5kb/s that can commercial QKD system provides on the monomode fiber of approximately 25 kilometers of length.In order to compare, representational classical communication system provides the message transmission rate of about 10Gb/s on the optical fiber of approximately 1000 kilometers of length.Suppose these parameters of QKD and classical system, can find need to be in QKD speed and/or transmission range remarkable improvement.
Summary of the invention
According to principle of the present invention, by being suitable for, by ripple (frequently) point multiplexing communication system for quantum-key distribution (QKD), solving the problems of the prior art.In one embodiment, communication system of the present invention comprises the transmitter that is coupled to receiver through transmission link.This transmitter comprises (i) first frequency comb source (OFCS), is suitable for generating first group of multiple evenly spaced frequency component; (ii) the first multi-channel optical modulator, is suitable for modulating independently first group of multiple each component to generate quantum information (QI) signal that is applied to transmission link.Receiver comprises (i) the 2nd OFCS, is suitable for generating second group of multiple evenly spaced frequency component; (ii) the second multi-channel optical modulator, is suitable for modulating independently second group of multiple each component to generate local oscillator (LO) signal.Each reference (reference) frequency standard (for example Cs atomic clock) independently in the first and second frequency comb source, so that the frequency component being generated by these comb sources has substantially the same frequency.Receiver uses multichannel homodyne detector, is suitable for processing the interference signal generating by combination LO signal and QI signal to determine the quantum information by QI signaling bearer.Advantageously, can configure communication system of the present invention to have and the comparable gathering of Ethernet bit rate (suing for peace) QKD speed on all channels.
According to a kind of embodiment, the present invention is a kind of communication system for transmission of quantum information, comprise the transmitter that is coupled to receiver through transmission link, wherein: this transmitter comprises the first light source that is coupled to the first optical modulator, wherein this first optical modulator is suitable for modulating the light being generated by the first light source to generate quantum information (QI) signal that offers transmission link; Comprise with receiver the secondary light source that is coupled to the second optical modulator, wherein: this second optical modulator is suitable for modulating the light being generated by secondary light source to generate local oscillator (LO) signal; The QI signal receiving with this LO signal of combination and through transmission link is to determine the quantum information by QI signaling bearer.
According to another kind of embodiment, the present invention is the transmitter for quantum information transmission in communication system, this transmitter comprises the first light source that is coupled to the first optical modulator, wherein this first optical modulator is suitable for modulating the light being generated by the first light source to generate quantum information (QI) signal, wherein: this communication system comprises the receiver that is coupled to transmitter through transmission link; By QI signal application in transmission link; Comprise with receiver the secondary light source that is coupled to the second optical modulator, wherein: the second optical modulator is suitable for modulating the light being generated by secondary light source to generate local oscillator (LO) signal; The QI signal receiving with this LO signal of combination and through transmission link is to determine the quantum information by this QI signaling bearer.
According to another embodiment, the present invention is the receiver for quantum information transmission in communication system, this receiver comprises the secondary light source that is coupled to the second optical modulator, wherein: this second optical modulator is suitable for modulating the light being generated by secondary light source to generate local oscillator (LO) signal; This communication system comprises the transmitter that is coupled to receiver through transmission link, this transmitter comprises the first light source that is coupled to the first optical modulator, and wherein the first optical modulator is suitable for modulating the light being generated by the first light source to generate quantum information (QI) signal that offers transmission link; The QI signal receiving through transmission link with this LO signal of combination and by receiver is to determine the quantum information by this QI signaling bearer.
According to another embodiment, the present invention is a kind of method of transmission of quantum information, comprising: the light that modulation is generated by the first light source on the transmitter of communication system is to generate quantum information (QI) signal; Through transmission link, this QI signal is sent to the receiver of described communication system; The light that modulation is generated by secondary light source on receiver is to generate local oscillator (LO) signal; With this LO signal of combination with the QI signal that receives on receiver through transmission link to determine the quantum information by this QI signaling bearer.
Brief description of the drawings
According to following detailed description, claims and accompanying drawing, it is more apparent that other aspects, features and advantages of the present invention will become, in the accompanying drawings:
Fig. 1 schematically illustrates quantum-key distribution (QKD) system of prior art.
Fig. 2 A-B schematically illustrates the representative phase modulation format and the corresponding homodyne detection statistics that are respectively used to the system of QKD shown in Fig. 1;
Fig. 3 schematically illustrates the QKD system according to an embodiment of the present invention;
Fig. 4 A-B illustrates the characteristic features of the frequency comb source (OFCS) that can use according to the QKD system of Fig. 3 of an embodiment of the present invention; With
Fig. 5 illustrates according to the method for the deviation frequency of OFCS shown in the survey map 4 of an embodiment of the present invention.
Embodiment
Refer at this alleged " a kind of embodiment " or " embodiment " specific features, structure or the feature that this embodiment of combination that can comprise describes at least one embodiment of the present invention.The identical embodiment of the inevitable all fingers of the phrase " in one embodiment " occurring in various piece in this manual, discrete or alternate embodiment is not repelled other embodiment mutually yet.
Fig. 1 schematically illustrates quantum-key distribution (QKD) system 100 of prior art.More specifically, system 100 comprises the transmitter 110 (Alice) and the receiver 150 (Bob) that are coupled through optical fiber 190.Design system 100 is to be used phase-modulation and homodyne detection to send quantum information.For each quantum bit, transmitter 100 generates two correlated optical pulses (compared with weak pulse punching with compared with hard pulse) by suitably cutting apart the output signal being generated by laser diode (LD).Each weak pulse rushes to have and is suitable for the quantum level of intensity (for example some photons of every pulse) of QKD and carries out phase-modulation by pulse modulator PM1.The phase-modulation of this weak (quantum) pulse has two objects: (1) selects the baseset for the Alice of corresponding quantum bit; (2) coding quantum bit values.Each hard pulse has (for example every pulse about 10 of typical strength grade
6photon), not at the interior phase-modulation of transmitter 110.The mutual time delay of these pulses, for example as illustrated on the input coupler 188 of Fig. 1 inner fiber 190, weak (quantum) pulse tail is with strong (classics) pulse, and is coupled in optical fiber.
After occurring on the output coupler 192 of optical fiber 190, these pulses enter receiver 150, be wherein reversed in the time delay between pulse, and pulse becomes interim aligning.(classics) pulse is via the phase-modulator PM2 phase-modulation in receiver 150 by force, and this phase-modulation is served the object of the baseset of selecting the Bob for measuring the quantum bit values of being carried by corresponding weak (quantum) pulse.Should be understood that weak (quantum) pulse is not at the interior phase-modulation of receiver 150.In beam splitter 160, combine spatially these pulses, beam splitter 160 is divided into obtained light signal subsequently two (interference) subsignals and each subsignal is sent to one of corresponding in photoelectric detector 170a-b.Each photoelectric detector 170a-b measures the intensity of the subsignal that receives and the output of result electricity is offered to differentiating amplifier 180.Amplifier 180 extracts the difference of two outputs, is amplified, and will send to signal processor (not shown) for the amplifying signal of further processing.
Beam splitter 160, photoelectric detector 170a-b on receiver 150 carry out homodyne detection scheme together with amplifier 180.This scheme provides the orthogonal measuring of weak (quantum) pulse (quantum-information signal), can determine the quantum bit values of encoding in this pulse according to this measurement.Should be understood that in this measurement, strong (classics) pulse is used as to local oscillator (LO).In the people's such as T.Hirano paper Phys.Rev.A the 68th volume the 42331st page (2003), can find additional firmware unit (for example polarizer (POL), polarization beam splitter (PBS), attenuator (ATT), part mirror (HM) and half-sum quarter-wave plate) in system 100 interior uses and the description of their corresponding functions thereof, its instruction is incorporated herein by reference.
Fig. 2 A-B diagram is respectively used to representative phase modulation format and the corresponding homodyne detection statistics of system 100.Referring to Fig. 2 A, transmitter 100 (Alice) uses phase-modulator PM1 (Fig. 1) by select randomly, for the phase shift α of coherency states, quantum bit values is coded in to weak (quantum) pulse from 0,90,180 and 270 degree, and wherein 0 is relevant with phase shift phase shift and the binary zero relevant to binary one and 180 and 270 degree of 90 degree.Receiver 150 (Bob) is selected randomly the phase shift for phase-modulator PM2 (Fig. 1) from 0 and 90 degree, and these phase shifts are applied to (classics) pulse by force.Therefore,, for every pair of (quantum and classics) pulse, system 100 generates relative phase shift φ=φ
a-φ
b, wherein φ
aand φ
bit is respectively Alice and Bob's phase shift.
Noiseless classical pulsed homodyne detection (using term " classics " to refer to that two pulses all have classical strength grade), the amplifier that is similar to the amplifier 180 of system 100 generates and 2E
se
lOthe proportional certainty output of cos φ, wherein E
sand E
lOit is respectively the electric field of information signal and local oscillator.Thereby for φ=0 and 180 degree, amplifier generates the output respectively with standardized value 1 and-1.Similarly, for φ=90 and 270 degree, amplifier generates the output with standardized value zero.
Because (quantum) pulse a little less than the interior use of system 100 represents the fact of information signal (and strong (classics) pulse as local oscillator signals), even if the output of amplifier 180 is not also uncertain in noisy situation, but the quanta fluctuation that described by available suitable probability-distribution function affects.Fig. 2 B diagram is when being used for describing when the photon average of weak (quantum) pulse is 1 photon of every pulse the representative probability-distribution function of the output of amplifier 180.More specifically, in Fig. 2 B, transverse axis X represents the normalization output of amplifier 180, and longitudinal axis P represents output probability.Curve 210 is and φ=0 ° corresponding probability-distribution function; Curve 220 is probability-distribution functions corresponding with φ=90 and 270 °; With curve 230 be and φ=180 ° corresponding probability-distribution function.Each probability-distribution function has gaussian shape, and centered by corresponding classical standard value.
Should be understood that curve 220 describes the probability-distribution function for φ=90 and 270 °.For these relative phase shifts, Bob can not determine by Alice and is coded in the quantum bit values in quantum-information signal, because Bob has selected the wrong i.e. baseset different from the selected baseset of Alice.But Bob can distinguish φ=0 ° and φ=180 °, because curve 210 and 230 is different.In this case, Alice and Bob have selected same baseset.
The representative signal processing of being carried out by Bob can comprise two threshold values, X are set
+and X
-, wherein X
+≤ X
-.If the normalization output X of amplifier 180
nbe greater than X
+, Bob judges phi=0 °.If X
nbe less than X
-, Bob judges phi=180 °.If Xn is between X
+and X
-between, Bob obtains indecisive result and abandons this judgement.Should be understood that Bob's judgement is always incorrect, and has intrinsic error probability because curve 210 and 230 has overlapping region.There is the fact of the nonzero probability of following situation in the reflection of this inherited error probability: (i) in the time of Bob judges phi=0 °, real φ value be 180 ° with (ii) when Bob judges phi=180 °, real φ value is 0 °.
After sending the pulse of right quantity from Alice to Bob, the authentication common signal channel of Bob through having set up for example informed his baseset selection of Alice on routine call or computer network, and Alice informs which selection of Bob is provided for determining the correct baseset of quantum bit values.Bob abandons subsequently the measurement result corresponding with incorrect baseset and explains remaining measurement result according to the modulation format of Fig. 2 A.Finally, Alice and Bob use decryption execution error correction and secret amplification procedure to extract safe dose sub-key.For example, at (1) F.Grosshans and P.Grangier, Phys.Rev.Letters, 2002, V0l.88, N.5, p.057902; (2) F.Grosshans and P.Grangier, arXiv:quant-ph/0204127 v1,22 Apr2002; (3) M.A.Nielsen and I.L.Chuang, " Quantum Computationand Quantum Information ", Cambridge University Press (2000), in pp.582-603, can find the additional information relevant with secret amplification procedure to representative error correction, it is all instructed and is incorporated herein by reference.
Refer again to Fig. 1, a key character of system 100 is from transmitter 110 along optical fiber 190 to receiver 150 transmitting locally oscillator signal (classical pulsed) together with information signal (quantum pulse).In classical communication, from transmitter to receiver, the known alternative of transmission LO signal is to provide tunable light source and phase-locked loop (PLL) at receiver, and this PLL is configured to the optical signal frequency being generated by light source and phase place to lock onto frequency and the phase place of information signal.PLL is conventionally measured difference frequency (beat frequency) and the phase shift between the signal of communicating by letter (information) signal and generated by tunable light source simultaneously and (ii) suitable feedback is offered to tunable light source (it forces this light source that these parameters are remained in regulation boundary) by (i), carries out work.But, can be applicable to common quantum communications and particularly in the quantum limit of system 100, measuring frequency and phase place need to be measured two non-exchanges (non-commuting) orthogonal (variable) simultaneously, and it is forbidden by quantum-mechanical general principle.In order to illustrate, beat measurement is similar to the measurement of energy difference (Δ E), and phase-shift measurement is similar to the measurement of time interval Δ t, and its measurement is subject to Heisenberg's uncertainty relation
control, wherein
it is Planck's constant.An actual influence of this basic uncertainty relation in system 100 is in quantum limit, and it is impossible on receiver 150, having locking in the LO frequency of suitable accuracy and phase place.Because this limits substantially, can not use the receiver with independence (second) light source being driven by conventional PLL to realize system 100.As above explained, configuration-system 100 to be to be transferred to receiver 150 by LO signal from transmitter 110 on the contrary, the LO signal transmitting owing to sending from same light source (LD Fig. 1) phase place and Frequency Locking to quantum-information signal.
In addition the fact that, local oscillator signals is sent to receiver 150 from transmitter 110 makes system 100 substantially incompatible with multichannel QKD transmission.For example, supposing the system 100 is supported in two QKD channels of the upper work of two different wave lengths (frequency).So, the essential transmission of optical fiber 190 strong (classics) LO pulse corresponding with each channel.Mutual for fear of the nonlinear optical in optical fiber 190, for example and LO pulse corresponding to different Q KD channel between, on input coupler 188, must cut apart these pulses temporarily.But, because the light velocity in optical fiber 190 depends on the fact of wavelength, the pulse corresponding with different channels with friction speed along spread fiber.Therefore,, even if cut apart at the beginning these pulses temporarily, for example, due to the length long (some kilometers or longer) of optical fiber 190, very fast mobile pulse finally may be caught up with its slow mobile pulse of following in optical fiber at the beginning.In the time that overlapping pulses are propagated along optical fiber 190, for example mix and Cross-phase Modulation through four ripples, so these overlapping pulses are non-linearly mutual, this causes harmful inter-channel crosstalk alternately.Adversely, this is crosstalked may increase the error rate of system 100 significantly, if do not destroy the QKD performance of this system completely.
Fig. 3 schematically illustrates the QKD system 300 according to an embodiment of the present invention.More specifically, system 300 comprises the transmitter 310 (Alice) and the receiver 350 (Bob) that are coupled through optical fiber 390.In one embodiment, system 300 is suitable for using the phase-modulation of the system 100 interior uses that are similar to Fig. 1 and homodyne detection to send quantum information.But, a difference between system 100 and 300 is that the former uses same light source (LD on transmitter 110) to generate quantum information and LO signal, and design the latter is to use two discrete light sources, lay respectively at the frequency comb source 320a-b on transmitter 310 and receiver 350.More specifically, on transmitter 310, use frequency comb source (OFCS) 320a to generate one or more quantum-information signal, subsequently by its channeling and being coupled in optical fiber 390.On receiver 350, use OFCS 320b to generate one or more local oscillator signals, use it for subsequently the homodyne detection of carrying out the corresponding quantum-information signal being received from transmitter 310 through optical fiber 390 by receiver.Therefore, different from system 100, system 300 is not from Alice to Bob's transmitting locally oscillator signal.
System 300 can avoid system 100 (explaining) substantially to limit above, because each frequency comb source 320a-b can generate the optical frequency with accuracy like this, thereby no longer needs the conventional Frequency Locking of OFCS 320b to OFCS 320a.For example, in one embodiment, OFCS 320 provides frequency comb, and wherein each frequency mode has (i) approximately 10kHz or narrower width and (ii) be positioned at apart from the about 100Hz of assigned frequency or the centre frequency of scope still less.Advantageously, these feature back-up systems 300 of OFCS 320 are carried out the homodyne detection of the one or more quantum-information signal on receiver 350, and do not transmit one or more LO signals from transmitter 310 to receiver.In addition, do not make system 300 can carry out multichannel QKD transmission from transmitter 310 to the fact of receiver 350 transmitting locally oscillators.More specifically, owing to transmitting the distance shorter (for example, lower than about 1 meter) of the stronger LO signal starting on the OFCS 320b in receiver 350 in same optical fiber along it, with compared with in the single channel QKD of this system configuration, the nonlinear optical in this optical fiber between these signals does not increase the error rate of system 300 alternately significantly.
Fig. 4 A-B illustrates according to the characteristic features of the OFCS 320 of an embodiment of the present invention.More specifically, in the embodiment shown in fig. 4, OFCS 320 is the mode locked laser with controlled carrier envelope migration (CEO) phase place.
Fig. 4 A diagram is by such one pulse train that uses the representative mode locked laser of CEO phase control to generate.More specifically, be shown in three continuous impulses in this sequence, solid line represents that electric-field carrier and dotted line represent corresponding pulses envelope.Envelope peak to peak separation between pulse (τ) is 1/f
rep, wherein f
repit is pulse recurrence rate.As Fig. 4 A can find out, be inconstant at the peak-to-peak relative phase of ripple of pulse envelope and bottom electric-field carrier, and change along with pulse.For example, for pulse 401, the crest of pulse envelope is aimed at the crest of electric-field carrier, and relative phase is zero.But, for pulse 402, change over Δ at the crest of pulse envelope and the peak-to-peak relative phase of nearest ripple of electric-field carrier
; With for pulse 403, this relative phase further increases Δ
become 2 Δs
.This pulse to pulse phase evolution mainly due to this group and the phase velocity different fact in mode locked laser chamber.But advantageously, thousand current part per trillion laser technique second are supported CEO phase increment (Δ
) effective control and stability to generate measurable and reproducible phase evolution.
The frequency spectrum that Fig. 4 B diagram is corresponding with the pulse train of Fig. 4 A.More specifically, vertical solid line represents the pattern of the frequency comb corresponding with the pulse train of Fig. 4 A, and bell curve represents frequency comb envelope.Should be understood that in frequency domain, the output of CEO phase controlled mode locked laser is equal to the array output of relevant continuous wave (CW) laser set substantially, and described relevant continuous-wave laser is the corresponding frequencies pattern of generated frequency comb respectively.Vertical dotted line diagram frequency grid grid nf in Fig. 4 B
rep, wherein n is positive integer.As shown in Figure 4 B, the frequency comb being generated by CEO phase controlled mode locked laser needn't be aimed at this frequency grid (grid), but conventionally with respect to a deviation frequency of this grid skew, δ=Δ
f
rep/ 2 π, with each frequency (f in following equation (1) description frequency comb
n):
f
n＝nf
rep+δ (1)
A result of the relation being provided by equation (1) is phase increment (Δ
) control be provided for the effective means of optical frequency absolute value in control frequency comb.The additional detail that for example can find CEO phase controlled mode locked laser feature in the people's such as D.J.Jones Science the 288th volume mat woven of fine bamboo strips 635 pages (2000), its instruction is incorporated herein by reference.
Other embodiments of the invention can be used the OFCS source except CEO phase controlled mode locked laser, even if the latter can provide following advantage (i) self-reference, distribute to the performance of individually defined thing Ricoh conversion by the light comb frequency of non-locking; (ii) because octuple is crossed over frequency spectrum, can be used for the wider bandwidth of QKD.For example, to lock onto the mode locked laser of referencing atom conversion be acceptable OFCS to the one-component in its frequency comb.Similarly, locking onto the single frequency laser of referencing atom conversion, for example, by its output of the optical modulator Sine Modulated driving in higher (radio frequency) frequency, is another acceptable OFCS.
Fig. 5 illustrates according to the method for the measurement deviation frequency (δ) of an embodiment of the present invention.The method of Fig. 5 can be applied octuple crossover frequency comb conventionally, and for example can be used for the output of correctly reference and the corresponding CEO phase controlled mode locked laser of control.More specifically, according to the method for Fig. 5, use second harmonic to generate (SHG) unit 504 light frequency corresponding with m the pattern (wherein m is positive integer) starting from the lower frequency side of octuple crossover frequency comb 502 doubled.The second harmonic obtaining has frequency f
sH=2f
m=2mf
rep+ 2 δ.The 2m pattern phase mutual interference of second harmonic and the high frequency side from frequency comb 502 subsequently, this 2m pattern has frequency f
2m=2mf
rep+ δ.This interfere generation has difference frequency f
sH-f
2mthe signal (beat tone) of=δ.Thereby, by measuring the frequency of this beat tone (beat note), can monitor the deviation frequency of CEO phase controlled mode locked laser.So that group and the phase velocity in this laser chamber to be set, so that this frequency comb is correctly located with respect to frequency grid, can adjust the value of δ by configuration laser.In one embodiment, can use the method for Fig. 5 to make two or more frequency comb 502 referencing atom clocks that generated by different frequency comb source to set up for example about 100Hz or the better alignment accuracy for the frequency comb source 320a-b in system 300.For example in the people's such as R.Holzwarth IEEE J.Quant.Electron the 37th volume mat woven of fine bamboo strips 1493 pages (2001), can find the more details about the atomic clock reference of CEO phase controlled mode locked laser, its instruction is incorporated herein by reference.
Refer again to Fig. 3, in one embodiment, each frequency comb source 320a-b comprises the CEO phase controlled mode locked laser (not shown) with reference to selected atomic clock frequency, for example described above.Transmitter 310 comprises multichannel phase-modulator 330, is configured to have multiple channels corresponding to a class frequency of the frequency comb generating with next free OFCS 320a.Modulator 330 comprises: (I) variable multiplexer/demultiplexer (MUX/DMUX) 334, is configured to receive through light circulator 332 output of OFCS 320a; (II) phase-shifter 336, couples light to MUX/DMUX.A function of MUX/DMUX 334 is that the comb frequency being generated by OFCS 320a is demultiplexed into discrete beams and these wave beams are sent to phase-shifter 336.Another function of MUX/DMUX 334 is to receive the phase shift wave beam that returns from phase-shifter 336, gives again multiplexingly, and consequential signal is offered to light circulator 332.
In one embodiment, phase-shifter 336 comprises the MEMS array of removable mirror, for example, be similar in U.S. Patent No. 6876484 disclosedly, and it is incorporated by reference in this text examines.More specifically, can change independently the each mirror in this array according to the control signal being provided by controller 338, the respective beam receiving from MUX/DMUX334 with this mirror of serving as reasons is introduced the phase shift of expecting, this phase shift and this mirror are proportional with respect to the displacement of reference position.In representational configuration, phase-shifter 336 is well-suited for each wave beam and introduces the light phase shift corresponding with the modulation format of Fig. 2 A.More specifically, according to the control signal of carrying out self-controller 338, the each mirror in phase-shifter 336 these mirror array of location is so that result phase shift is one of 0,90,180 and 270 degree substantially.For each time slot, from these values, select randomly phase shift to encode corresponding bit value for each wave beam, and within the duration of this time slot, keep stable, 0 is relevant with phase shift phase shift and the binary zero relevant to binary one and 180 and 270 degree of 90 degree.Alice's the selection of the baseset for corresponding quantum bit is determined in selected phase shift.
Should be understood that the mirror array from light circulator 332 to phase-shifter 336 and reverse round trip, twice of the light signal corresponding with this comb frequency is through MUX/DMUX334.Because MUX/DMUX334 is variable MUX/DMUX, can configure it with by the each attenuated optical signal desired amount in respective channel, and irrelevant with the decay of introducing in other channel.Therefore, MUX/DMUX334 can provide balanced light signal (for example converting the initial bell frequency comb envelope being generated by OFCS 320a to substantially smooth shape) and the additional function of quantum grade that the light intensity decays in each channel is become to be suitable for QKD transmission.Subsequently, light circulator 332 sends to pulse to whittle device 340 phase shift/the deamplification receiving from MUX/DMUX334, and it becomes pulse train by these signal shapings and result is coupled in optical fiber 390.Suitably lock-out pulse whittles device 340 and phase-shifter 336, for example, to whittle the position of pulse corresponding to the intermediate point of corresponding time slot.In representational configuration, this time slot duration was approximately 100 nanoseconds, and each width that whittles pulse is about 10 picoseconds.
Whittling by pulse the pulse train that device 340 generates is frequency (wavelength) multiplexed quantum-information signal with the multiple components corresponding with the channel of phase-modulator 330.Be chosen in the decay of introducing in MUX/DMUX334 so that the photon numbers of the every pulse of every component is suitable for the QKD agreement in system 300 interior uses.For example, for (known in the prior art) BB84 and B92 agreement, photon numbers is approximately 1 photon of the every pulse of every component.Alternately, for continuous variable agreement, photon numbers is the about hundreds of photon of the every pulse of every component.
Receiver 350 comprises multichannel phase-modulator 360, and it is substantially similar to the multichannel phase-modulator 330 of transmitter 310.More specifically, phase-modulator 360 comprises that light circulator 362, MUX/DMUX364, phase-shifter 366, controller 368 and pulse whittle device 370, and its light circulator 332, MUX/DMUX334, phase-shifter 336, controller 338 and pulse that is similar to respectively phase regulator 330 whittles device 340.But a difference between phase-modulator 330 and 360 is that the latter also has multichannel polarization controller 372.A reason that comprises polarization controller 372 in phase-modulator 360 is that the polarization of the quantum-information signal that generated by transmitter 310 may be along with the propagation of signal in optical fiber 390 and change.Polarization controller 372 is for being aligned in the polarization of the each LO component starting on OFCS 320b and the polarization of the respective component of the quantum-information signal receiving.
In one configuration, in order to be identified for the correct polarization setting of polarization controller 372, the training signal with known sequence of quantum bits that transmitter 310 sends for each channel.Receiver 350 uses polarization setting that this training signal adjusts each channel correctly to aim at the polarization and corresponding quantum information component of LO component subsequently.For example, receiver 350 is measured the orthogonal variable of each pulse, and the phase place of LO signal pulse displacement 90 degree one by one.If known quantum bit sequence has substantially the same pulse, the quadratic sum of the measurement orthogonal variable of continuous impulse
the amplitude that is parallel to the quantum signal polarizing LO field with its polarization is proportional.Can control each frequency component of polarization controller 372 with the polarization of the each frequency component in rotation LO field, thus the polarization of aiming at the quantum signal of corresponding frequencies.Once determine correct polarization setting, configure polarization controller 372 to fix these settings in the duration of QKD dialogue.Can repeat at any time as required this program aims to ensure good and correct polarization.
The each LO component being generated by OFCS 320b and phase-modulator 360 has classical strength grade and (for example whittles by pulse every pulse 10 that device 370 whittles
6individual photon).According to the luminous power being generated by OFCS 320b, phase-modulator 360 interior may need to amplify some or all comb frequency (with decling phase in phase-modulator 330 to).Therefore, phase-modulator 360 can merge one or more image intensifers (not shown) and comprise the MUX/DMUX 364 that is configured to introduce alap decay.
In the time that transmitter 310 uses the modulation format shown in Fig. 2 A, the phase-shifter 366 in configuration phase modulator 360 is to locate each mirror in its mirror array, so that result phase shift is one of 0 and 90 degree substantially.For each time slot, from these two values, select randomly phase shift for each channel and select with the baseset for determine the bit value being carried by the respective component of quantum-information signal in this time slot that Bob is provided.Therefore,, for each component of the quantum-information signal receiving from transmitter 310, phase-modulator 360 outputs are suitable for carrying out on receiver 350 the many components LO signal being substantially similar in the homodyne detection scheme of system 100 interior execution.
As above explained, the pinpoint accuracy that optical frequency generates in frequency comb source 320a-b makes system 300 needn't carry out the Frequency Locking of LO signal to quantum-information signal.But, still need to the phase place between these signals lock the expectation phase shifts of 0 and 90 degree of the component of supporting phase-modulator 360 to be provided for exactly LO signal.Carry out by overall phase-modulator 354 and phase-shifter 366 work that LO signal phase is locked onto to quantum-information signal.For example, for LO component phase being locked onto to the respective component of quantum-information signal, the training signal with known sequence of quantum bits that transmitter 310 sends for each channel.Subsequently, receiver 350 uses this training signal to adjust the mirror position in phase-shifter 366, so that for each signal component, the relative phase difference between LO and quantum-information signal is for example 90 degree.
In the time that system 300 is switched to QKD transmission from training sequence transmission, receiver 350 uses mirror position definite in training sequence process as with reference to position, generates suitable mirror displacement to generate the phase shift of determining that quantum bit values needs with respect to it.Overall situation phase-modulator 354 is the selectable units that can contribute to maintain this phase place locking after use phase-shifter 366 is realized the locking of initialization phase place.More specifically, because different comb frequencies is all relative to each other, the variation of the additive phase at interchannel that may occur along with the time is also that be correlated with and definite conventionally.Therefore additional (overall situation) phase shift that, is common to all frequencies (channel) to introduce by configuring overall phase-modulator 354 can compensate these additive phases and change.
The LO signal generating by the quantum-information signal receiving through optical fiber 390 from transmitter 310 with by OFCS 320b and phase-modulator 360 offers three-dB coupler 352, and it combines these signals, subsequently result is divided into two interference sub-signals.Subsequently, each interference sub-signals is offered to one of corresponding in demodulation multiplexer 374a-b, this interference sub-signals is demultiplexed into each spectrum component by it.Then, use every antithetical phrase signal component with same frequency to carry out the homodyne detection that is substantially similar to execution in the receiver 150 (Fig. 1) of system 100.More specifically, receiver 350 comprises two photodetector array 376a-b of the array 380 that is coupled to Change sensitive amplify device.The photoelectric detector that receives same frequency in array 376a-b is received to the respective amplifier in array 380 through the photoelectric detector connecting terminals with opposite polarity.Therefore, this amplifier is effectively as the differentiating amplifier that is configured to the signal difference that amplifies photoelectric detector.The differential signal of this amplification is offered to signal processor 382 further to process.
In one configuration, by for example explaining difference signal according to the threshold method of describing with reference to figure 2B above, processor 382 is processed the difference signal corresponding with each frequency.After the quantum information transmission time slot of about determined number, Bob informs Alice through authentication common signal channel, and he selects the baseset for each frequency, and Alice informs which selection of Bob is provided for determining the correct baseset of quantum bit values.Subsequently, Bob abandons the measurement result corresponding with wrong baseset and explains remaining measurement result according to the modulation format of Fig. 2 A.Finally, Alice and Bob's execution error correction and secret amplification procedure to extract safe dose sub-key from decryption.
In one embodiment, design system 300 is to have following characteristics: (i) channel (frequency) interval of about 10GHz; (ii) 256 channels altogether, corresponding to the about spectral bandwidth of 20nm; (iii) modulating speed of about 10MHz, corresponding to the time slot duration of about 100ns; (iv) the quantum-information signal intensity of about 1pW/ channel; (v) the LO signal strength signal intensity of about 1mW/ channel.In the time using these parameters to carry out, system 300 is supported the QKD speed higher than 20Mb/s, and its speed providing with respect to the QKD system by prior art has a significant improvement.In another kind of embodiment, wherein system 300 is used full octuple to cross over optical range (for example, from 1000 to 2000nm), and 10GHz channel spacing is assembled QKD speed and can be reached about 1Gb/s.Advantageously, this gathering QKD speed can provide comprehensive encryption support for the communication system of working on current ethernet speed.
Although described with reference to an illustrative embodiment the present invention, this description can not be interpreted as limitation.For example, do not comprise variable MUX/DMUX334, can use conventional MUX/DMUX and the discrete multichannel attenuator that is coupled to this MUX/DMUX to realize phase-modulator 330.Alternately or additionally, can configure phase-shifter 336 with attenuate signal components, for example, by tilting mirrors or change its reflectivity and/or shape.In addition, can be by two separate units, the DMUX that is configured to only to carry out the MUX of multiplexing function and is configured to only carry out demultiplexing function, alternative arrangements for example, to carry out multiplexing and single MUX/DMUX (MUX/DMUX334 or MUX/DMUX364) demultiplexing function simultaneously.Each assembly can be embodied as to waveguide circuit or free space optical unit.Alternately or additionally, can be applied to phase-modulator 360 by similarly revising.Can use the optical modulator except the modulator based on MEMS, the modulator that for example uses the array of single lithium niobates modulator unit, the conventional modulator unit in InP waveguide modulator unit or InP surface to realize.Can configuration-system 300 to use various QKD protocol operations, for example, without any restriction, BB84 agreement, B92 agreement or continuous variable agreement.Although reference phase modulation has been described the present invention, it will be appreciated by those skilled in the art that when also can using amplitude modulation(PAM) or phase place and amplitude, modulation realizes the present invention.Can distribute neatly and dynamically and use the addressable QKD bandwidth resources of frequency comb source to support some different transmitter-receivers configurations, for example (i) is coupled to a transmitter of a receiver, as shown in Figure 3; (ii) be coupled to a transmitter of two or more receivers, configure this receiver to use the different subsets of the comb frequency being used by this transmitter; (iii) be coupled to one or more transmitters of single receiver, configure this transmitter to use the different subsets of the comb frequency being used by this receiver; (iv) be coupled to multiple transmitters of multiple receivers, between these transmitter and receivers, suitably distribute comb frequency.Can use the OFCS source different from CEO phase controlled mode locked laser.In addition, can use light source to realize some embodiment of the present invention, described light source is suitable for generating single frequency (wavelength), and this frequency is reference frequency standard suitably.In the situation that not departing from the scope of the present invention with principle, can use various frequency standards (for example atomic clock type).For the technical staff who the present invention relates in field, the various amendments of apparent described embodiment and other embodiments of the invention can be considered as within the principle and scope of the present invention, described in claims.
For the object of this specification, MEMS equipment is the equipment that comprises the two or more parts that are suitable for relatively moving, and wherein this moves based on any suitable mutual or combination of interactions, and for example machinery, heat, electricity, magnetic, light and/or chemistry are mutual.But use can comprise the small or less manufacturing technology (comprising miniature (nano) manufacturing technology) that must not be limited to following technology and manufacture MEMS equipment: (1) self-assembly technology, is for example used self-assembly individual layer, has and expect the immersion coating of chemical substance high affinity and manufacture and the infiltration of the Chemical Felter that dangles; (2) use the pattern of such as imprint lithography, optics evaporation, material to draw and select wafer/material processed technology of processing, shaping, plating and the structure processing etc. on etching and surface.In MEMS equipment, the size/scale of some unit can be so to allow the demonstration of quantum effect.But the example of MEMS equipment comprises the equipment of NEMS (micro-electromechanical systems) equipment that is not restricted to, MOEMS (low-light electro-mechanical system) equipment, micro-machine, micro-system and use microsystems technology or the integrated generation of micro-system.
Although described the present invention in the situation that MEMS equipment is implemented, can in any size, implement the present invention in theory, comprise the size that is greater than micro-dimension.
With particular order, the step in following claim to a method is described although use corresponding mark, if present, unless but the description of claim hint is carried out the concrete order of some or all steps, will these steps not be restricted to this particular order execution.
Claims (10)
1. for a communication system for transmission of quantum information, comprise the transmitter that is coupled to receiver through transmission link, wherein:
Described transmitter comprises the first light source that is coupled to the first optical modulator, and wherein said the first optical modulator is suitable for modulating the light being generated by the first light source to generate the quantum information QI signal that is applied to transmission link; With
Described receiver comprises the secondary light source that is coupled to the second optical modulator, wherein:
Described the second optical modulator is suitable for modulating the light being generated by secondary light source to generate local oscillator LO signal;
Described receiver is configured to, by described LO signal and the QI signal combination receiving through transmission link, to produce interference signal, and determine the quantum information by described QI signaling bearer based on described interference signal.
2. according to the communication system of claim 1, wherein:
Described LO signal transmits without transmission link; With
Described receiver is suitable for LO signal phase to lock onto QI signal.
3. according to the communication system of claim 1, wherein the each light source in the first and second light sources is with reference to a frequency standard.
4. according to the communication system of claim 1, wherein:
The first light source comprises the first frequency comb source OFCS that is suitable for generating first group of multiple evenly spaced frequency component;
Described the first optical modulator is suitable for modulating independently first group of each frequency component in multiple and selects with coding quantum bit and the baseset that is provided for described transmitter; With
Described QI signal comprises at least one subset of first group of modulating frequency component in multiple.
5. according to the communication system of claim 4, wherein:
Secondary light source comprises the 2nd OFCS that is suitable for generating second group of multiple evenly spaced frequency component;
Described the second optical modulator is suitable for modulating independently second group of each frequency component in multiple and selects with the baseset that is provided for described receiver; With
Described LO signal comprises at least one subset of second group of modulating frequency component in multiple.
6. according to the communication system of claim 5, wherein:
First group of modulating frequency component in multiple and second group of modulating frequency component in multiple have public frequency collection;
Described system comprises the optical coupler that is adapted to pass through combination LO signal and QI signal and generates the first and second interference signals; With
Described receiver comprises the multichannel homodyne detector that is suitable for processing interference signal, wherein:
For the each frequency in common set, homodyne detector is suitable for measuring the strength difference between the first and second interference signals, and measurement result is applied to signal processor; With
Described signal processor is suitable for according to measurement result growing amount sub-key.
7. according to the communication system of claim 6, wherein, for the each frequency in common set, described signal processor is suitable for:
In each time slot, according to the baseset comparison that is described Slot selection by transmitter and receiver, accept or refuse corresponding measurement result; With
Compile described quantum key according to accepted result.
8. according to the communication system of claim 5, wherein each the comprising in the first and second optical modulators:
Be suitable for the frequency component that demultiplexing receives from corresponding OFCS multiplexer/demultiplexer MUX/DMUX and
The MEMS array of removable mirror, wherein:
Each mirror in described array is suitable for receiving the frequency component of demultiplexing, and wherein said mirror is used for the phase shift of described frequency component with respect to the location positioning of reference position; With
Described MUX/DMUX is also suitable for the frequency component of multiplexing phase shift to generate corresponding QI or LO signal.
9. the transmitter in the communication system for transmission of quantum information, comprises the first light source that is coupled to the first optical modulator, and wherein said the first optical modulator is suitable for modulating the light being generated by the first light source to generate quantum information QI signal, wherein:
Described communication system comprises the receiver that is coupled to transmitter through transmission link;
By QI signal application in transmission link; With
Described receiver comprises the secondary light source that is coupled to the second optical modulator, wherein:
Described the second optical modulator is suitable for modulating the light being generated by secondary light source to generate local oscillator LO signal; With
Described receiver is configured to, by described LO signal and the QI signal combination receiving through transmission link, to produce interference signal, and determine the quantum information by described QI signaling bearer based on described interference signal.
10. the receiver in the communication system for transmission of quantum information, comprises the secondary light source that is coupled to the second optical modulator, wherein:
The second optical modulator is suitable for modulating the light being generated by secondary light source to generate local oscillator LO signal;
Described communication system comprises the transmitter that is coupled to receiver through transmission link;
Described transmitter comprises the first light source that is coupled to the first optical modulator, and wherein said the first optical modulator is suitable for modulating the light being generated by the first light source to generate the quantum information QI signal that is applied to transmission link; With
Combine described LO signal and the QI signal receiving through transmission link by receiver, to produce interference signal, and determine the quantum information by described QI signaling bearer based on described interference signal.
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| US68172605P | 2005-05-17 | 2005-05-17 | |
| US60/681,726 | 2005-05-17 | ||
| US11/210,973 US20060263096A1 (en) | 2005-05-17 | 2005-08-24 | Multi-channel transmission of quantum information |
| US11/210,973 | 2005-08-24 | ||
| PCT/US2006/015587 WO2006124208A1 (en) | 2005-05-17 | 2006-04-25 | Multi-channel transmission of quantum information |
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| CN101176297B true CN101176297B (en) | 2014-09-03 |
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| CN102158285B (en) * | 2011-04-18 | 2013-10-02 | 武汉邮电科学研究院 | Method and device for producing paths of coherent light carriers |
| CN103227718A (en) * | 2012-12-31 | 2013-07-31 | 安徽问天量子科技股份有限公司 | Integrated controller and control method for controlling sending and receiving of quantum secret key |
| CN106197496A (en) * | 2013-11-21 | 2016-12-07 | 充梦霞 | A kind of laser sensor frequency division multiplexing device using photodetector |
| CN103929251B (en) * | 2014-04-22 | 2017-05-24 | 华南师范大学 | Low noise QKD and WDM classic communication network compatible method and device |
| US9705599B2 (en) * | 2015-07-30 | 2017-07-11 | Google Inc. | Systems for improved spectral efficiency in multi-carrier communication systems |
| CN108737082B (en) | 2017-04-24 | 2020-11-17 | 华为技术有限公司 | Signal receiving device and receiving method |
| WO2019032106A1 (en) * | 2017-08-09 | 2019-02-14 | Google Llc | Frequency pattern for reducing parasitic interactions in a qubit grid |
| CN111401561B (en) * | 2020-03-04 | 2022-05-20 | 清华大学 | Quantum calculating device |
| CN111327369B (en) * | 2020-03-13 | 2021-07-02 | 电子科技大学 | Frequency domain multiplexing quantum channel basic link of optical fiber communication waveband |
| CN111510207B (en) * | 2020-04-15 | 2023-03-21 | 中国人民解放军国防科技大学 | Source end light intensity fluctuation testing method in quantum key distribution system |
| CN111901042B (en) * | 2020-08-11 | 2022-03-11 | 中国电子科技集团公司第四十四研究所 | Phase modulation-based large dynamic signal demodulation model method |
| CN112737673B (en) * | 2020-12-28 | 2023-11-03 | 重庆邮电大学 | Method and device for optical detection of transient weak microwave signal spectrum under noise |
| CN112887033B (en) * | 2021-05-06 | 2021-08-24 | 北京中创为南京量子通信技术有限公司 | CV-QKD system and quantum key distribution method |
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| US20040208643A1 (en) * | 2002-05-13 | 2004-10-21 | Ar Card | Coherent optical receivers |
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