CN101176298B - Phase lock in multi-channel quantum communication system - Google Patents
Phase lock in multi-channel quantum communication system Download PDFInfo
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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 title that the application requires on May 17th, 2005 to submit to is the U.S. Provisional Patent Application No.60/681 of " Auantum Keydistribution ", 726 priority.The theme of this application relate to the application mutually the title submitted to of same date be the U.S. Patent application No.xx/xxx of " Multi-ChannelTransmission of Quantum Information ", 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 that is used to use the quantum cryptography transmitting encrypted data.
Background technology
Usually 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 that uses in conjunction with this algorithm.Usually, privacy key is selected at random, only sends and the known sufficiently long bit sequence of recipient.For example, in symmetric encryption scheme, dispatching station uses secret key encryption information and enciphered data is sent to receiving station on common signal channel.Receiving station uses same key to decipher this encryption subsequently and recovers raw information.
The long more then system of key is safe more, 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 the possibility key value to crack outside the DES, do not have more efficiently method.Yet,, still can crack DES if the listener-in has powerful computing ability.Therefore, in order to realize higher fail safe, can use single sheet (one-time pad) (promptly the same long key) with transmission message.Although using the communication system of single sheet is safe with respect to the attack based on absolute computing capability in theory, a kind of like this system must handle so-called encryption key distribution problem, promptly safely key is offered the problem of transmission/receiving station.
Use conventional (typically) cipher key transmission methods, it may be by listener-in's PASSIVE SURVEILLANCE, the difficult physical security measures that sends certifiable privacy key and need trouble usually.Yet, use the quantum technology can realize that privacy key distributes.More specifically, in quantum cryptography, send privacy key by the specified quantitative subchannel, the fail safe of described quantum channel is based on principle of quantum mechanics.More specifically, suitably the quantum state of system is revised in any measurement of the quantized system of selecting inevitably, and this is well-known.Therefore, when the listener-in attempts by carry out measuring when quantum channel obtains information, validated user can detect the fact of having carried out measurement, and therefore it will abandon all and jeopardize safe key.
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, perhaps (ii) train of coherent optical pulses, comprise a small amount of (it is individual for example to be lower than hundreds of) photon respectively, with the quadrature value coded key bit of the selected variable that characterizes each pulse.The title of disclosed the 74th volume 145-195 page or leaf N.Gisin, G.Ribordy, W.Tittel and H.Zbinden is for finding to set up and use the more details of typical amount subchannel in the comment of " Quantum Cryptography " in Reviews ofModern Physics in 2002, and its instruction is incorporated herein by reference.
Make certain gains although be used for the equipment of quantum channel in exploitation, this equipment does not still reach performance objective, for example on quantum-key distribution (QKD) speed and transmission range.For example, the current approximately QKD speed of 1.5kb/s that can commercial QKD system be provided on the about 25 kilometers monomode fiber of length.For relatively, representational classical communication system provides the message transmission rate of about 10Gb/s on the about 1000 kilometers optical fiber of length.Suppose these parameters of QKD and classical system, can find need be on QKD speed and/or transmission range remarkable improvement.
Summary of the invention
According to principle of the present invention, be coupled to receiver and be suitable for dividing the multiplexing communication system that is used for the transmitter of quantum-key distribution (QKD) solution the problems of the prior art ripple (frequently) by comprising through transmission link.In one embodiment, this receiver comprises optical modulator (OM), homodyne detector and signal processor.This OM is suitable for the local oscillator that generates on receiver (LO) signal is carried out phase shift.Homodyne detector is suitable for (i) combination LO signal and quantum information (QI) signal that receives from transmitter through transmission link to generate two interference signals; (ii) measure the strength difference between these interference signals.Processor is suitable for handling measurement result to generate control signal, and its one or more phase shifts that cause generating in OM are to be based upon the phase locking between LO and the QI signal.In a kind of configuration, the QI signal has (i) a plurality of pilot frequency components, carries training signal and (ii) a plurality of QKD component respectively, respectively carry quantum key data; Have corresponding pilot tone and QKD frequency component with the LO signal.Receiver is adapted to pass through and uses each the pilot frequency components phase shift to the LO signal of the reference phase shift determined as frequency component according to the corresponding training signal of QI signal, the pilot frequency components of phase locking QI and LO signal.This receiver also is adapted to pass through approximate reference phase shift that use derives according to the reference phase shift of pilot frequency components and to each QKD frequency component phase shift of LO signal, the QKD frequency component of phase locking QI and LO signal.Advantageously, system of the present invention can keep the phase locking to the QKD frequency component of QI and LO signal, and the QKD frequency component of QI signal carry quantum key data continuously.
According to a kind of embodiment, the present invention is a kind of method that receives quantum information on the receiver of communication system, this communication system comprises the transmitter that is coupled to receiver through transmission link, and this method comprises: (A) receive quantum information (QI) signal that uses first light source to generate by transmitter through transmission link; (B) local oscillator (LO) signal phase that will use secondary light source to generate locks onto this QI signal.
According to another kind of embodiment, the present invention is a kind of receiver that is used for communication system, this communication system is suitable for transmission of quantum information and comprises the transmitter that is coupled to receiver through transmission link, and wherein this receiver is suitable for: (i) receive quantum information (QI) signal that uses first light source to generate by transmitter through transmission link; Local oscillator (LO) signal phase that (ii) will use secondary light source to generate locks onto this QI signal.
According to another embodiment, the present invention is a kind of communication system that is used for transmission of quantum information, comprise the transmitter that is coupled to receiver through transmission link, wherein this receiver is suitable for: (i) receive quantum information (QI) signal that uses first light source to generate by transmitter through transmission link; Local oscillator (LO) signal phase that (ii) will use secondary light source to generate locks onto this QI signal.
Description of 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 the multichannel quantum communication system according to an embodiment of the present invention;
Fig. 2 diagram is according to the phase modulation format that can use in the system of Fig. 1 of an embodiment of the present invention;
Fig. 3 A-C diagram is used for the representative homodyne detection statistics of the modulation format of Fig. 2 during to quantum information (QI) signal when the phase locking correctly of local oscillator (LO) signal on the receiver in system shown in Figure 1;
Fig. 4 A-C diagram is used for the representative homodyne inspection statistics of the modulation format of Fig. 2 on the receiver in system shown in Figure 1 when having phase-lock error between LO and QI signal;
Fig. 5 diagram is according to the method that the LO signal phase is locked onto the QI signal on the receiver of system shown in Figure 1 of an embodiment of the present invention; With
Fig. 6 A-C and 7A-C illustrate the representative embodiments of method shown in Figure 5.
Embodiment
Be meant concrete feature, structure or the feature in conjunction with this embodiment description that at least a embodiment of the present invention, can comprise at this alleged " a kind of embodiment " or " embodiment ".The phrase that occurs in the various piece " in one embodiment " must all not refer to identical embodiment in this manual, and discrete or alternate embodiment is not repelled other embodiment mutually yet.
Fig. 1 schematically illustrates the multichannel quantum communication system 100 according to an embodiment of the present invention.More specifically, system 100 is suitable for dividing the multiplexing quantum-key distribution (QKD) that is used for ripple (frequently).System 100 comprises transmitter 110 (Alice) and the receiver 130 (Bob) through transmission link (for example optical fiber) 120 couplings.Transmitter 110 has the frequency comb source (OFCS) 112 that is coupled to optical modulator (OM) 116.OFCS 112 generates the light signal 114 with a plurality of even spaced frequency components.OM 116 is suitable for the multi-channel optical modulator of each frequency component of separate modulated signals 114 with generated frequency multiplexed quantum-information (QI) signal.This QI signal is applied to transmission link 120 by OM 116 and receives as QI signal 128 on receiver 130.
Receiver 130 comprises common be similar to the respectively OFCS 112 of transmitter 110 and OFCS 132 and the OM 136 of OM116.OFCS 132 generates the light signal 134 with a plurality of even spaced frequency components, OM 136 independently each component of modulation signal 134 to generate multiplexing local oscillator (LO) signal 138.Each frequency comb source 112 and 132 is reference frequency standard (for example atomic clock) independently, so that the group of frequencies that signal 114 and 134 has substantially the same (public).For example, in one embodiment, each frequency comb source 112 and 132 provides frequency comb, and wherein each frequency mode has (i) about 10kHz or better spectrum width and (ii) is positioned at respect to frequency standard distance about 100Hz of defined assigned frequency or centre frequency more among a small circle.Developed in recent years and can implement this light source, for example used carrier envelope skew (CEO) locked laser.Therefore, QI signal 128 and LO signal 138 have the frequency component that belongs to substantially the same group of frequencies.Yet, a difference between signal 128 and 138 be the former have be suitable for QKD than low-intensity, and the latter has higher-strength.For example, in a kind of configuration, QI signal 128 and LO signal 138 have every pulse per minute amount about 1 and 10 respectively
6The intensity of photon.
Fig. 2 diagram is according to the phase modulation format that can use in system 100 of an embodiment of the present invention.More specifically, by in OM 116, randomly the phase shift of 0,90,180 or 270 degree being applied to each frequency component of signal 114,0 is relevant with the phase shift of 90 degree phase shift and binary systems " 0 " relevant with binary one and 180 and 270 degree, and transmitter 110 (Alice) is coded in quantum bit values on the QI signal that offers transmission link 120.For each quantum bit, except the encoding ratio paricular value, the baseset selection of this bit of Alice is also determined in phase shift.For example, the modulation format of Fig. 2 comprises two orthogonal basis set (basis set), and baseset has along the phase shifting state of reality (Re) axle (promptly 0 with 180 degree states) and another baseset and has shifting state mutually (i.e. 90 and 270 degree states) along void (Im) spool.Thereby if the Alice selects one of 0 and 180 degree phase shifts, then the Alice has selected the baseset corresponding with real axis.Alternately, if the Alice selects one of 90 and 270 degree phase shifts, then the Alice has selected orthogonal basis set (promptly corresponding to the imaginary axis).On receiver 130 (Bob), by in OM 136, randomly the phase shift of 0 or 90 degree being applied to each frequency component of signal 134, use the LO oscillator signal 138 that is obtained to carry out above-mentioned homodyne detection scheme subsequently, determine quantum bit values by 128 carryings of QI signal.For each quantum bit, the baseset selection of this bit of Bob is determined in the phase shift of using in OM 136 similarly.
Fig. 3 A-C diagram is when the representative homodyne detection statistics that the 138 about phase lockings of LO signal is used for modulation format shown in Figure 2 during to QI signal 128 on receiver 130.More specifically, Fig. 3 A illustrates planisphere, four circles 302,304.306 and 308 surround and the most probable zone that may be fallen into by the corresponding phase vectors of Alice's quantum bit of QI signal 128 carryings.Bigger with the zone that these circles are represented, because (1) QI signal 128 is influenced with (2) because the further decentralized photo bit vector of noise in the system 100 by quanta fluctuation.If the Alice has selected reality (Re) baseset of specific quantum bit, then when the quantum bit was " 1 ", the phase vectors most probable corresponding with this bit fell into circle 302, perhaps when the quantum bit is " 0 ", falls into circle 306.Alternately, if the Alice has selected void (Im) baseset, then when the quantum bit was " 1 ", the phase vectors most probable corresponding with this bit fell into circle 304, perhaps when the quantum bit is " 0 ", falls into circle 308.The projection of phase vectors on Bob's selected baseset (Re or Im) that Bob's the homodyne detection scheme of carrying out in receiver 130 is equal to measurement basically and is received.If average on the quantum bit of abundant quantity, the standardization output of each amplifier in the array 160 is then described with probability-distribution function, for example be similar to shown in Fig. 3 B-C.
If Bob's selected baseset is identical with Alice's baseset, then be extracted in the measurement of the projection formation possibility quantum bit values on this baseset.Curve 320 shown in Fig. 3 B is described the probability-distribution function that the standardization amplifier when the Alice selects identical baseset with the Bob is exported with 360 representatives.More specifically, curve 320 representatives probability-distribution function and curve 360 representatives and " 0 " bit corresponding probability-distribution function corresponding with " 1 " bit.Curve 320 and 360 has Gaussian-like shapes, and is center (promptly having 1 and-1 distribution average respectively) with 1 and-1 respectively.Should be understood that the Bob can distinguish binary one and " 0 ",, and separate fully mutually because curve 320 is different with 360.Therefore, " correct baseset is selected " that usually this situation is called the Bob.
If Bob's selected baseset is different from Alice's baseset, then take projection on Bob's baseset do not constitute may quantum bit values measurement.The probability-distribution function of the standardization amplifier output when the Alice selects different baseset with the Bob is described in curve 348 representatives shown in Fig. 3 C.Should be understood that, different with Fig. 3 B, present single curve (curve 348) is represented two probability-distribution functions, and promptly corresponding with " 1 " bit probability-distribution function and overlapping with the corresponding probability-distribution function of " 0 " bit, this curve are that Gauss is the center similarly with 0.Because this probability-distribution-function degeneracy, the Bob can not distinguish binary one and " 0 ", usually the situation of Fig. 3 C is called Bob " selection of mistake baseset ".
If Alice and Bob select their baseset that is used for each bit randomly, then the probability of outcome distribution function of being measured by the Bob is three camel-back curves, is similar to the curve of representing curve 320,348 and 360 (Fig. 3 B and 3C) sum.As described in greater detail below, can in training mode, obtain each probability-distribution function with each curve 320,348 and 360 representatives.
In a kind of configuration, according to the detection statistics shown in Fig. 3 B-C, receiver 130 (Bob) description below measurement result.Signal processor 170 is set up two threshold values, X for each channel
+And X
-, X wherein
-≤ X
+, X
-And X
+Value is identical or different for different channels.If the standardization amplifier of channel output X
nGreater than X
+, then the Bob is " 1 " bit with corresponding quantum bit decision.If X
nLess than X
-, then the Bob is judged as " 0 " bit with this quantum bit.If X
nBetween X
+And X
-Between, then the Bob obtains uncertain result and abandons judgement.In a kind of configuration, for each channel, X
+=X
-=0.
From the Alice after the Bob sends the quantum bit of right quantity, the Bob tells the Alice that his baseset is selected by the checking common signal channel of for example setting up on routine call or computer network, and it is correct that the Alice tells which baseset of Bob to select.The Bob preserves subsequently with this correct baseset and selects corresponding judgement, selects corresponding judgement and abandon with wrong baseset, thus compiling side-play amount sub-key (being also referred to as primary key).At last, Alice and Bob use side-play amount sub-key execution error correction and secret amplification procedure to extract the safe dose sub-key.For example at (1) F.Grosshans and P.Grangier, Phys.Rev.Letters, 2002, Vol.88, N.5, p.057902; (2) F.Grosshans and P.Grangier, arXiv:quant-ph/0204127 v1,22 Apr 2002; (3) M.A.Nielsen and I.L.Chuang, " Quantum Computation and Quantum Information ", Cambridge University Press (2000), can find the additional information relevant with secret amplification procedure among the PP.582-603, all be incorporated herein by reference with representative error correction.
Fig. 4 A-C diagram is used for the representative homodyne detection statistics of modulation format shown in Figure 2 on receiver 130 when having phase-lock error between LO signal 138 and QI signal 128.Fig. 4 A-C is similar to Fig. 3 A-C basically respectively, represents similar accompanying drawing unit with the mark with identical back two digits.Shown in Fig. 4 A, the phase-lock error of 0 degree cause most probable zone that Alice's phase vectors falls into respect to Bob's coordinate system around coordinate center anglec of rotation θ.Select as the Bob under the situation of the baseset identical with the Alice, curve 420 and 460 (Fig. 4 B) is compared more close mutually with curve 320 and 360 (Fig. 3 B), and is the center with 1 and-1 no longer respectively.When Bob's selection was selected different basesets with the Alice, rotation caused the degeneration more serious than the probability-distribution-function degeneracy of Fig. 3 C.More specifically, when Alice and Bob selected different basesets and phase-lock error to exist, the probability-distribution function corresponding with " 1 " and " 0 " bit was no longer by representing with the curve 348 similar superimposed curves of Fig. 3 C.On the contrary, these two probability-distribution functions are represented with the curve 420 and 460 that is similar to Fig. 4 B, but have more closely-spaced two different curves (not shown in Fig. 4 C) between them.Fig. 4 C diagram is represented the curve 450 of the cumulative distribution function of two quantum bit values.Curve 450 has dual (doublet) shape, and this is the serious sign of degenerating.
Comparison diagram 4B and Fig. 3 B find that curve 420 and 460 has than curve 320 and 360 bigger overlapping.The overlapping of this increase may increase the wrongheaded quantity of Bob, because there is the probability that increases: (i) when the Alice sends " 0 " bit, X
n＞X
+(ii) when the Alice sends " 1 " bit, X
n＜X
-In order to keep misjudgment quantity lower, therefore wish in system 100, between LO signal 138 and QI signal 128, to keep correct phase locking, as shown in Figure 3.
Refer again to Fig. 1 simply, the processor 170 of receiver 130 is suitable for generating the control signal 180 that offers OM 136.According to control signal 180, OM 136 sets up the reference phase shift of each frequency component that is used for LO signal 138 correctly this component phase is locked onto the corresponding frequencies component of QI signal 128.Subsequently, with respect to the reference phase shift of setting up for this component, be applied in the 0 and 90 degree random phase shifts that are applied to each frequency component in the QKD transmission course in the OM 136.The method of the generation control signal 180 of the exemplary embodiments according to the present invention will be described hereinafter in more detail.
Fig. 5 diagram generates the method 500 of control signal 180 on the receiver 130 of system 100 according to an embodiment of the present invention.In the step 502 of method 500, the transmitter 110 of system 100 and receiver 130 are configured to send respectively and receive and comprise the training signal of training bit sequence.Usually, training sequence can comprise transmitter 110 and receiver 130 any predetermined bit combinations known and that use known baseset selection to send.For example, in a kind of configuration, training sequence is included in the modulation format of Fig. 2 the string with the binary one of 0 degree phase-shift coding.Usually, training sequence long enough (for example 1000 bits) for processor 170 for example is similar to Fig. 3 and Fig. 4 is illustrated to have enough data generating probability distribution functions.Can upward or at selected some pilot carrier frequencies (channel) go up the transmission training sequence in each frequency (channel) of system 100.When only pilot carrier frequency being used for the training sequence transmission, transmit concurrently with training sequence, other frequency (being called the QKD frequency hereinafter) can be continued on for the transmission of convention amount subkey data.In representational configuration, system 100 comprises a pilot carrier frequency that is used for per nine QKD frequencies.
In the step 504 of method 500, processor 170 is handled the quadrature measurement results of each frequency of using and is thought that each frequency in these frequencies generates corresponding probability-distribution function in the training sequence transmission.In a kind of configuration, processor 170 can use sliding window to handle with the probability-distribution function along with each frequency of time tracking.For example, suppose that the Bit String length in training sequence is 1000 bits.Then can configuration processor 170 to generate (i) first probability-distribution function based on the quadrature measurement results corresponding with the 1st to the 100th bit; (ii) based on second probability-distribution function of the quadrature measurement results corresponding with the 11st to the 110th bit; (iii) based on the 3rd probability-distribution function of the quadrature measurement results corresponding with the 21st to the 120th bit; Or the like.Therefore, for the whole training sequence of 1000 bits, processor 170 generates 91 probability-distribution functions, any phase shift adjustment that changes and/or carry out in OM 136 when the time that it is put time-out reflection link and channel status.
In the step 506 of method 500, processor 170 is one or more probability-distribution functions that each frequency estimation generates in step 504.This assessment can comprise average, the intermediate value of determine distributing, the whole bandwidth (FWHM) on half maximum, or the like.According to this assessment, processor 170 generates control signals 180, and the reference phase shift value that its indication OM 136 was provided with or adjusted each frequency is with the respective component of phase locking LO signal 138 and QI signal 128 correctly.In a kind of configuration, processor 170 uses above-mentioned sliding window to handle with the phase locking of (partly) real-time tracking between LO signal 138 and QI signal 128.
In all frequencies being used for the configuration of training sequence system for transmitting, system 100 is switched between training and QKD operator scheme termly.In training mode, system 100 for example sets up the phase locking that is used for each frequency as described above.In the QKD pattern, system 100 uses phase locking traffic volume subkey data on all frequencies of setting up in training mode.The mode switch cycle in system 100 is controlled by the situation of transmission link 120 usually.For example, when when the ambient temperature of transmission link 120 stablize, appearance more continually of the mode switch in the system 100.On the contrary, when the ambient temperature along transmission link 120 was subjected to than great fluctuation process, the mode switch in the system 100 can occur more continually.Should be understood that the QKD agreement can comprise that error rate monitors the part as its error correction and secret amplification procedure, when link quality changed along with the time, the dynamic adjustment of this support mode switching cycle.
Pilot carrier frequency is being used for the configuration of training sequence system for transmitting, processor 170 is preferably followed the tracks of the phase locking between LO signal 138 and QI signal 128 that is used for each pilot tone in real time.For all other signal frequencies, by the current reference phase shift value approximate (for example interpolation and/or extrapolation) from being used for this pilot tone, processor 170 is determined reference phase shift (preferably also being real-time).For example, in a kind of configuration, processor 170 will be considered as one group of discrete sampling of continuous function for the reference phase shift value that this pilot tone is determined, this continuous function is described the frequency dependence for the reference phase shift of all signal frequencies.Subsequently, processor 170 use selected fitting technique (for example spline-fit) calculate this continuous function and the function that calculated of on suitable frequency, sampling to be identified for the reference phase shift of the signal frequency except pilot tone.
If suitable or essential, can configuration-system 100 changing over different distribution as the current demand signal Frequency Distribution of pilot tone and QKD frequency.For example,, the signal frequency of lesser amt can be appointed as pilot tone, for example with total QKD capacity of raising system 100 for metastable Link State.On the contrary,, the signal frequency of larger amt can be appointed as pilot tone, for example the accuracy of following the tracks of with the phase locking that improves the QKD frequency for unsettled relatively Link State.Must not be identical entirely at the frequency interval between the adjacent pilot frequencies on the bandwidth of system 100.As the case may be, compare, can distribute per unit bandwidth still less or the more pilot frequency for some spectral regions with other spectral regions and/or system as a whole 100.
The representative embodiments of Fig. 6 A-C and Fig. 7 A-C graphic technique 500.More specifically, Fig. 6 A-C diagram when suitably with 138 phase lockings of LO signal during, for the channel of the system 100 that is configured to send training sequence, the representative homodyne detection statistics on receiver 130 to QI signal 128.Similarly, Fig. 7 A-C diagram is when existing phase-lock error, for the representative homodyne detection statistics of this channel between LO signal 138 and QI signal 128.Fig. 6 A-C and Fig. 7 A-C are similar to Fig. 3 A-C and Fig. 4 A-C basically respectively, represent similar accompanying drawing unit with the mark with identical back two digits.The training sequence corresponding with Fig. 6 A-C and Fig. 7 A-C comprises the string of the encoded binary in Fig. 2 modulation format " 1 " with 0 degree phase shift (Re axle).
Referring to Fig. 6, because training sequence only has binary one, Alice's phase vectors falls in the circle 602 basically.Because the Bob knows the Alice which baseset is used for training sequence,, the Bob selects the baseset identical or different with the Alice so controlling him fully.Curve 620 (Fig. 6 B) is if the expression Bob determines to select the baseset identical with the Alice (being the Re axle), the probability-distribution function that generates on the step 504 of method 500.Similarly, curve 640 (Fig. 6 C) is if the expression Bob determines to select the baseset different with the Alice (for example Im axle), at the probability-distribution function of step 504 generation.Curve 620 and 640 has Gaussian-like shapes and is respectively 1 and 0 distribution average.
Referring to Fig. 7 A, the phase-lock error of 0 degree causes being similar to the phase diagram rotation shown in Fig. 4 A.Curve 720 (Fig. 7 B) is if the representative Bob determines to select the baseset identical with the Alice now, the probability-distribution function that generates in the step 504 of method 500, with curve 740 (Fig. 7 C) if the representative Bob determines to select different basesets, the probability-distribution function that generates in this step.Because phase diagram rotation (Fig. 7 A), curve 720 (Fig. 7 B) and 740 (Fig. 7 C) have respectively distribution average (1-δ) and-Δ, wherein δ=1-cos θ and Δ=sin θ.Thereby, select for arbitrary baseset, the Bob can by measure distribution average respectively the departing from of distance 1 and 0 (perhaps be equal to ground, corresponding probability-distribution function is respectively with respect to 1 and 0 depart from) detected phase lock error.Yet the Bob is according to the Δ value but not the δ value generates control signal 180 is more favourable, because (1) measures departing from of curve 740 with respect to 0, therefore possible normalization errors is less to the influence of Δ value; (2) symbol of Δ can distinguish θ on the occasion of and negative value, δ then can not; (3) for the little value of θ, Δ is much larger than δ.Therefore, when processor 170 according to Δ but not δ when generating control signal 180, receiver (Bob) may be realized better phase locking (being less phase-lock error).
According to this observation, in a kind of configuration, system 100 can following manner of execution 500.For step 502, configuring receiver 130 (Bob) is to select and the baseset of selecting to be used for transmitting at training sequence the basis set orthogonal of each frequency of using on transmitter (Alice) 110.For step 504, configuration processor 170 for example uses above-mentioned " sliding window " to handle with the generating probability distribution function.For step 506, configuration processor 170 is zero to generate control signal 180 for use in the distribution average of each frequency of training sequence transmission.Subsequently, will be that the reference phase shift that is used for this frequency is appointed as in the zero corresponding phase shift in OM 136 with the distribution average that is used for characteristic frequency.Configuration processor 170 is suitably adjusted control signal 180 with continuation tracking distribution average zero in real time to handle according to " sliding window " of step 504, thereby suitably adjusts reference phase shift.
The enforcement that should be understood that method 500 produces reference phase shift, and it generates the 90 degree phase shifts of each frequency component of LO signal 138 with respect to the corresponding frequencies component of QI signal 128.Therefore, from spend, be chosen in the conventional QKD transmission and be applied to the random phase shift of each frequency component, thereby obtain to spend phase shift 0 and 90 phase shifts of spending respectively with respect to 0 of modulation format shown in Figure 2 by OM 136 with respect to reference phase shift-90 and 0.
When starting the transmission of QI signal 128 (Fig. 1) first, receiver 130 (Bob) is not known the input signal phase place at the beginning.In order to obtain this initial knowledge, configuring receiver 130 is promptly determined the corresponding relation between phase shift of introducing and the phase place of the importing the QI signal with calibration OM 136 in OM.In a kind of configuration, receiver 130 is carried out calibration procedure, it relates to for each frequency component carries out the scanning of being introduced the phase-shift value of LO signals 138 on such as the phase shift at interval of 2 π by OM 136, use enough little relative phase shift increment, receive training signal simultaneously and follow the tracks of corresponding distribution average.The scanning curve as a result that distribution average is illustrated as the phase shift function of being introduced should have two null values, can be used as the calibration point of OM 136.Subsequently, receiver 130 (Bob) is according to one or many scanning result initialization LO phase place and begin to follow the tracks of phase-lock error, has described as mentioned.
In a kind of configuration, system 100 can followingly be reduced in training sequence and measure the time quantum of going up cost.System 100 can be increased in photon numbers in one or more training signals (increase and improve indistinctively under the prerequisite of the linearity of different frequency interchannel and/or nonlinear crosstalk at this) temporarily.This increase helps receiver 130 to measure one or more probability-distribution functions in time slot still less, thereby reduces the whole training time.
In addition, can set up the initial phase lock training signal measurement result of a plurality of pilot channels afterwards to be combined in by configuring receiver 130.More specifically, if the combined spectral spread of all quantum channels less (for example about 1nm) and/or the length of transmission link 120 are shorter, then can suppose because the interim phase change of all channels that variations in refractive index causes in the transmission link is correlated with, thereby describe all a plurality of pilot channels with individual probability distribution function integral body.Therefore, can be configured on all quantum channels, introduce simultaneously the single global phase shifter that identical phase place is adjusted with use by configuring receiver 130, thereby simplify the processing that maintains phase locking between QI and the LO signal.On the other hand, if the combined spectral spread of all quantum channels length big and/or transmission link 120 is longer, then the interim phase change of different channels is different and unique.Therefore, though still be correlated with, need to adjust respectively the phase place corresponding with different quantum channels.
Though described the present invention with reference to an illustrative embodiment, this description can not be interpreted as limited significance.For example, can configuration-system 100 to use various QKD protocol operations, for example hard-core, BB84 agreement, B92 agreement or continuous variable agreement.Although reference phase modulation has been described embodiments of the invention, it should be appreciated by those skilled in the art that and also can revise the modulation of the present invention with any other suitable parameter of being used for polarization modulation or light signal.The light source position that is used to generate the LO signal needn't be limited to receiver (Bob), and in one embodiment, described light source can be positioned on transmitter (Alice) or other appropriate location.Although described embodiments of the invention with reference to the QKD transmission, person of skill in the art will appreciate that and can in other that uses the quantum message transmission used, use the present invention, for example quantum authentication procedures, secure financial transactions (quantum money), quantum games (optimal judgement that in the group consults, carries out), or the like.The conspicuous various modifications of describing embodiment and other embodiments of the invention will be regarded as within as the principle and scope of the present invention that claims limited for the present invention relates to those of skill in the art.
With particular order step in the following claim to a method is described although use corresponding sign, if present, unless but the description of claim hint is carried out the concrete order of some or all steps, then will these steps not be restricted to this particular order execution.
Claims (12)
1. method that is used for receiving quantum information at the receiver place of communication system, described communication system has the transmitter that is coupled to receiver through transmission link, and described method comprises:
(A) receive the quantum information QI signal that uses first light source to generate by transmitter through transmission link; With
(B) the local oscillator LO signal phase that will use secondary light source to generate locks onto the QI signal.
2. the method for claim 1 also comprises:
Combination LO signal and QI signal are to generate first and second interference signals;
The strength difference of measurement between first and second interference signals; With
According to measurement result the LO signal is carried out phase shift, to realize phase locking.
3. the process of claim 1 wherein:
For step (A), the QI signal comprises training signal; With
Step (B) comprising:
Generation is corresponding to the probability-distribution function of training signal;
Determine the reference phase shift of LO signal according to described probability-distribution function; With
Use described reference phase shift that the LO signal is carried out phase shift, to realize phase locking.
4. the method for claim 3, wherein step (B) comprising:
Determine the distribution average of probability-distribution function;
Determine reference phase shift according to described distribution average; With
Follow the tracks of the null value of described distribution average adaptively.
5. the process of claim 1 wherein that in QI and the LO signal each all has a plurality of frequency components, wherein:
At least one frequency component phase locking of LO signal is arrived the corresponding frequencies component of QI signal; With
Each frequency component of described QI signal is at the carrying training signal and have between the signal of quantum key data alternately.
6. the process of claim 1 wherein:
For step (A), the QI signal has one or more pilot frequency components, and each is characterized by corresponding light frequency, wherein each pilot frequency components carrying training signal;
For step (B), the LO signal comprises the one or more pilot frequency components with one or more light frequencies;
For each pilot frequency components of LO signal, step (B) comprising:
Determine reference phase shift according to training signal; With
Use described reference phase shift that the pilot frequency components of LO signal is carried out phase shift.
7. the method for claim 6, wherein at least one frequency component of the LO signal with the different signal frequency of one of light frequency with one or more pilot frequency components, step (B) comprises the reference phase shift of determining at least one frequency component of described LO signal according to one or more reference phase shift of determining for one or more pilot frequency components of LO signal.
8. the method for claim 6, wherein, except one or more pilot frequency components, in QI and the LO signal each has one or more quantum key distribution QKD frequency components, and wherein said method comprises uses described QKD frequency component and one or more training signal quantities received subkey data concurrently.
9. a communication system that is used for transmission of quantum information comprises the transmitter that is coupled to receiver through transmission link, and wherein said receiver is suitable for:
Receive the quantum information QI signal that uses first light source to generate by transmitter through transmission link; With
The local oscillator LO signal phase that uses secondary light source to generate is locked onto the QI signal.
10. the communication system of claim 9, wherein said receiver comprises:
Optical modulator is suitable for the LO signal is carried out phase shift;
Detector is suitable for (i) combination LO signal and QI signal to generate first and second interference signals; (ii) measure the strength difference between first and second interference signals; With
Processor is suitable for handling measurement result to generate control signal, and it disposes described optical modulator the LO signal is carried out phase shift, to realize phase locking.
11. a device that is used for receiving at the receiver place of communication system quantum information, described communication system has the transmitter that is coupled to receiver through transmission link, and described device comprises:
Receive the module of using the quantum information QI signal of first light source generation by transmitter through transmission link; With
The local oscillator LO signal phase that uses secondary light source to generate is locked onto the module of QI signal.
12. the device of claim 11, wherein:
The QI signal is the channeling QI signal with frequency component of more than first separate modulation; The LO signal has more than second frequency component, and described device is suitable for described more than first individual corresponding frequencies components are arrived at least one frequency component phase locking of described more than second.
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| US68172605P | 2005-05-17 | 2005-05-17 | |
| US60/681,726 | 2005-05-17 | ||
| US11/210,941 | 2005-08-24 | ||
| US11/210,941 US7706536B2 (en) | 2005-05-17 | 2005-08-24 | Phase locking in a multi-channel quantum communication system |
| PCT/US2006/015588 WO2006124209A1 (en) | 2005-05-17 | 2006-04-25 | Phase locking in a multi-channel quantum communication system |
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| CN101176298B true CN101176298B (en) | 2011-03-30 |
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| CN200680017099XA Expired - Fee Related CN101176298B (en) | 2005-05-17 | 2006-04-25 | Phase lock in multi-channel quantum communication system |
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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 |
| CN106197499A (en) * | 2013-11-21 | 2016-12-07 | 充梦霞 | Use pump light source and the laser sensor frequency division multiplexing device of fiber grating |
| 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 |
| CN116957087A (en) * | 2017-08-09 | 2023-10-27 | 谷歌有限责任公司 | Frequency mode for reducing parasitic interactions in quantum grids |
| 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 |
| CN115456182B (en) * | 2022-01-27 | 2024-06-14 | 本源量子计算科技（合肥）股份有限公司 | Device for generating qubit control signal and quantum computer control system |
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| JP3646561B2 (en) * | 1999-05-12 | 2005-05-11 | 日本電気株式会社 | Key distribution method using quantum cryptography |
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| US5245459A (en) * | 1989-05-25 | 1993-09-14 | British Telecommunications Public Limited Company | Optical communications systems |
| US5675648A (en) * | 1992-12-24 | 1997-10-07 | British Telecommunications Public Limited Company | System and method for key distribution using quantum cryptography |
| CN1477413A (en) * | 2003-06-30 | 2004-02-25 | 华南师范大学 | Quantum encoder whose polarization state is modulated by phase and decoder and its application |
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| CN101176297A (en) | 2008-05-07 |
| CN101176297B (en) | 2014-09-03 |
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