Relativistic quantum cryptography on “Arrested” photons

A new relativistic quantum cryptosystem is proposed in which the information is carried by the extended single-photon states with orthogonal polarizations and effective length exceeding the communication channel length. The light “arrest” effect is used as a procedure for the detection and preparation of extended states. The cryptosystem is secure against any eavesdropping attempts, because its states are quantized and the propagation velocity is limited. In this scheme, the preparation and detection procedures are local in space but require a finite time, depending on the extension of the states. The preparation for detecting at the receiver end begins before the state left the source at the input end.     

Iterative quantum algorithm for distributed clock synchronization

Clock synchronization is a well-studied problem with many practical and scientific applications.We propose an arbitrary accuracy iterative quantum algorithm for distributed clock synchronization using only three qubits.The n bits of the time difference between two spatially separated clocks can be deterministically extracted by communicating only O(n) messages and executing the quantum iteration process n times based on the classical feedback and measurement operations.Finally,we also give the algorithm using only two qubits and discuss the success probability of the algorithm.     

On the resistance of relativistic quantum cryptography in open space at finite resources

The security of keys for the basic nonrelativistic BB84 protocol has been examined for more than 15 years. A simple proof of security for the case of a single-photon source of quantum states and finite sequences has been only recently obtained using entropy uncertainty relations. However, the existing sources of states are not strictly single-photon. Since sources are not single-photon and losses in a quantum channel??open space??are not a priori known and vary, nonrelativistic quantum cryptographic systems in open space cannot guarantee the unconditional security of keys. Recently proposed relativistic quantum cryptography removes fundamental constraints associated with non-single-photon sources and losses in open space. The resistance of a fundamentally new family of protocols for relativistic quantum key distribution through open space has been analyzed for the real situation with finite lengths of transmitted sequences of quantum states. This system is stable with real sources of non-single-photon states (weakened laser radiation) and arbitrary losses in open space.     

Multiplex quantum cryptography based on time coding without interferometers

Three fundamentally new experimental prototypes of optical fiber quantum-cryptography schemes are described. They are appreciably simpler than the available prototypes, contain fewer optical fiber components, and do not require adjustment during key generation. These cryptosystems can naturally be called quantum time-shift cryptography. They realize the B92 protocol and use a pair of nonorthogonal single-photon states as information states. One such scheme does not use fiber-optic Mach-Zehnder interferometers and, therefore, provides natural realization of the multiplex secure-key distribution regime.     

What fundamentally new properties are introduced by special relativity to quantum cryptography in open space?

A fundamentally new relativistic quantum cryptography protocol has been proposed for key distribution through open space. The protocol guarantees the security of keys at any damping and for a nonstrictly single-photon source of quantum states.     

A scheme for implementing quantum clock synchronization algorithm in cavity QED

In this paper, we propose a scheme for implementing the quantum clock synchronization (QCS) algorithm in cavity quantum electrodynamic (QED) formalism. Our method is based on three-level ladder-type atoms interacting with classical and quantized cavity fields. Atom-qubit realizations of three-qubit and four-qubit QCS algorithms are explicitly presented.     

Relativistic algebraic spinors and quantum motions in phase space

Following suggestions of Schönberg and Bohm, we study the tensorial phase space representation of the Dirac and Feynman-Gell-Mann equations in terms of the complex Dirac algebra C₄, a Jordan-Wigner algebra G₄, and Wigner transformations. To do this we solve the problem of the conditions under which elements in C₄ generate minimal ideals, and extend this to G₄. This yields the linear theory of Dirac spin spaces and tensor representations of Dirac spinors, and the spin-1/2 wave equations are represented through fermionic state vectors in a higher space as a set of interconnected tensor relations.     

On a two-pass scheme without a faraday mirror for free-space relativistic quantum cryptography

The stability of destructive interference independent of the input polarization and the state of a quantum communication channel in fiber optic systems used in quantum cryptography plays a principal role in providing the security of communicated keys. A novel optical scheme is proposed that can be used both in relativistic quantum cryptography for communicating keys in open space and for communicating them over fiber optic lines. The scheme ensures stability of destructive interference and admits simple automatic balancing of a fiber interferometer.     

Wavelength synchronization technology for UDWDM-PON transmitter based on injection locking

We propose a concept of wavelength synchronization to ensure the stability of ultra-dense channels in an ultra-dense wavelength division multiplexing passive optical network(UDWDM-PON)transmitter.A mode-locked laser is used to provide wavelength references for users.By injection locking the semiconductor laser,the separation of the wavelength reference is realized in an optical line terminal.The downlink and uplink wavelength references are interlaced and distributed to facilitate the synchronization of uplink carriers.In the optical network unit,the uplink optical carriers are filtered by injection locking semiconductor lasers,which achieve wavelength synchronization for the uplink users.In this Letter,an adaptive wavelength synchronization transmitter for UDWDM-PON is realized with a channel spacing of 5 GHz.     

Realization of optoelectronic integrated transmitter and receiver for POF Applications

The optoelectronic integrated transmitter and receiver for 650 nm plastic optical fiber (POF) communication applications realized in 0.5 μm BCD (Biplor, CMOS and DMOS) process is first described in this paper. The 650 nm resonant cavity light emitting diode (RCLED) is used as light source. It is first proposed for optoelectronic integration of the transmitter by bonding RCLED to the driver chip. Temperature compensation technology is employed in the driver circuit to compensate for the modulation current. In the monolithic optoelectronic integrated receiver, large area multi-finger PIN photodetector (PD) that is compatible with standard IC process, transimpedance amplifier and post amplifier are presented. Measurement results show that the responsivity and capacitance of PD is 0.25 A/W and 5 pF, respectively. The sensitivity of receiver is −14.6 dBm at 180 Mb/s and BER is less than 10⁻⁹ for 650 nm input light by POF. A clear eye diagram is demonstrated for 180 Mb/s PRBS. These indicate that optoelectronic integrated chips can be employed in high-speed POF-based Fast Ethernet systems for broadband access network applications.     

On the complexity of search for keys in quantum cryptography

The trace distance is used as a security criterion in proofs of security of keys in quantum cryptography. Some authors doubted that this criterion can be reduced to criteria used in classical cryptography. The following question has been answered in this work. Let a quantum cryptography system provide an ε-secure key such that ½‖ρ_XE ? ρ_U ? ρ_E‖₁ < ε, which will be repeatedly used in classical encryption algorithms. To what extent does the ε-secure key reduce the number of search steps (guesswork) as compared to the use of ideal keys? A direct relation has been demonstrated between the complexity of the complete consideration of keys, which is one of the main security criteria in classical systems, and the trace distance used in quantum cryptography. Bounds for the minimum and maximum numbers of search steps for the determination of the actual key have been presented.     

On the justification of quantum cryptography based on time shifts

The security of quantum cryptography based on time shifts has been mathematically proved. The procedures of preparing and measuring the most strongly localized states with a support in a finite frequency band are described. It has shown that measurements of states in the finite frequency band and a finite time window are sufficient for detecting any change in input states. The use of available multiplex fiber optic systems based on an arrayed waveguide grating for time-shift quantum cryptography is briefly discussed.     

Entangled state quantum cryptography: eavesdropping on the ekert protocol

Using polarization-entangled photons from spontaneous parametric down-conversion, we have implemented Ekert's quantum cryptography protocol. The near-perfect correlations of the photons allow the sharing of a secret key between two parties. The presence of an eavesdropper is continually checked by measuring Bell's inequalities. We investigated several possible eavesdropper strategies, including pseudo-quantum-nondemolition measurements. In all cases, the eavesdropper's presence was readily apparent. We discuss a procedure to increase her detectability.     

脉冲激光引信发射接收模块的电磁干扰

针对脉冲激光引信应用于中小口径常规弹药过程,由于体积严格受限而造成引信内部电磁干扰严重的问题,结合发射、接收模块工作原理,说明在其内部采取电磁干扰抑制措施的必要性。通过分析发射、接收模块电磁干扰产生机理,提出采用双重屏蔽方法抑制辐射干扰,采用线性阻抗稳定网络、缓冲网络和共差模合成扼流圈结合的多重滤波技术抑制传导干扰。对各措施作用效果进行仿真与实验,结果表明：厚度为1.55 mm钢材料对辐射干扰具有良好屏蔽效果;接收模块输出干扰信号峰峰值减小至70 mV,约为原干扰信号的1/40。这些方法大幅度降低了脉冲激光引信内部的电磁干扰,且工作稳定可靠。     

脉冲激光引信发射接收模块的电磁干扰

 针对脉冲激光引信应用于中小口径常规弹药过程,由于体积严格受限而造成引信内部电磁干扰严重的问题,结合发射、接收模块工作原理,说明在其内部采取电磁干扰抑制措施的必要性。通过分析发射、接收模块电磁干扰产生机理,提出采用双重屏蔽方法抑制辐射干扰,采用线性阻抗稳定网络、缓冲网络和共差模合成扼流圈结合的多重滤波技术抑制传导干扰。对各措施作用效果进行仿真与实验,结果表明：厚度为1.55 mm钢材料对辐射干扰具有良好屏蔽效果;接收模块输出干扰信号峰峰值减小至70 mV,约为原干扰信号的1/40。这些方法大幅度降低了脉冲激光引信内部的电磁干扰,且工作稳定可靠。     

Effects of depolarizing quantum channels on BB84 and SARG04 quantum cryptography protocols

We report experimental studies on the effect of the depolarizing quantum channel on weak-pulse BB84 and SARG04 quantum cryptography. The experimental results show that, in real world conditions in which channel depolarization cannot be ignored, BB84 should perform better than SARG04 under the most general eavesdropping attack.     

Relativistic constraints on the distinguishability of orthogonal quantum states

The constraints imposed by special relativity on the distinguishability of quantum states are discussed. An explicit expression relating the probability of an error in distinguishing two orthogonal single-photon states to their structure, the time t at which a measurement starts, and the interval of time T elapsed from the start of the measurement until the time at which the outcome is obtained by an observer is given as an example.     

Development of the quantum discriminator for compact atomic clock

In the Laboratory of Frequency Standards, Quantum Radiophysics Division, Lebedev Physical Institute, a compact atomic standard of frequency and time is being developed. The results of this study make it possible to achieve a narrower metrological resonance of coherent population trapping (CPT) than in developed foreign analogues of compact atomic clocks, which will have a direct effect on the standard stability. The effect of the combination of buffer gas and antirelaxation coating on the CPT amplitude and resonance width are studied; parameters of short-cavity diode lasers (SCDLs) specially developed in collaboration with the Polyus Research and Development Institute are studied. A prototype of the compact physical discriminator for the atomic clock is developed and assembled. The dark width of the metrological resonance in the discriminator is less than 1 kHz, which theoretically implies the development of a compact atomic clock with a stability (Allan parameter) no worse than 3 · 10⁻¹² per hour.     

Simple estimate of the critical length of a quantum communication channel with attenuation for coherent-state quantum cryptography

For the B92 protocol with allowance for real attenuation and phase interruption of signal states in a one-dimensional optical fiber, a simple estimate is obtained for the critical length of the quantum communication channel that can provide secure key distribution.     

Simple delay scheme for quantum cryptography based on a Mach-Zehnder optic fiber interferometer

A simple experimental scheme is proposed for a relativistic quantum cryptosystem based on a Mach-Zehnder optic fiber interferometer. In this scheme, quantum mechanical laws, along with the restrictions imposed by the Special Relativity, ensure the detection of any eavesdropping attempt.