Local distinguishability of multipartite orthogonal quantum states

We consider one copy of a quantum system prepared in one of two orthogonal pure states, entangled or otherwise, and distributed between any number of parties. We demonstrate that it is possible to identify which of these two states the system is in by means of local operations and classical communication alone. The protocol we outline is both completely reliable and completely general; it will correctly distinguish any two orthogonal states 100% of the time.     

Local and global distinguishability in quantum interferometry

A statistical distinguishability based on relative entropy characterizes the fitness of quantum states for phase estimation. This criterion is employed in the context of a Mach-Zehnder interferometer and used to interpolate between two regimes of local and global phase distinguishability. The scaling of distinguishability in these regimes with photon number is explored for various quantum states. It emerges that local distinguishability is dependent on a discrepancy between quantum and classical rotational energy. Our analysis demonstrates that the Heisenberg limit is the true upper limit for local phase sensitivity. Only the "NOON" states share this bound, but other states exhibit a better trade-off when comparing local and global phase regimes.     

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.     

Single photon level spectrum measurement at fiber communication band using frequency up-conversion technology

We have developed a polarization independent (PI) spectrometer based on frequency up-conversion technology for single photon level spectrum measurement at the fiber communication band. To overcome the polarization dependence of the frequency up-conversion process, we use two periodically poled lithium niobate (PPLN) waveguides with a polarizing beam splitter. We experimentally study the sensitivity and resolution of the PI up-conversion spectrometer. We demonstrate the spectrometer by way of a spectrum measurement of a single photon level signal in the communication band.     

Single photon frequency up-conversion and its applications

Optical frequency up-conversion is a technique, based on sum frequency generation in a non-linear optical medium, in which signal light from one frequency (wavelength) is converted to another frequency. By using this technique, near infrared light can be converted to light in the visible or near visible range and therefore detected by commercially available visible detectors with high efficiency and low noise. The National Institute of Standards and Technology (NIST) has adapted the frequency up-conversion technique to develop highly efficient and sensitive single photon detectors and a spectrometer for use at telecommunication wavelengths. The NIST team used these single photon up-conversion detectors and spectrometer in a variety of pioneering research projects including the implementation of a quantum key distribution system; the demonstration of a detector with a temporal resolution beyond the jitter limitation of commercial single photon detectors; the characterization of an entangled photon pair source, including a direct spectrum measurement for photons generated in spontaneous parametric down-conversion; the characterization of single photons from quantum dots including the measurement of carrier lifetime with escalated high accuracy and the demonstration of the converted quantum dot photons preserving their non-classical features; the observation of 2nd, 3rd and 4th order temporal correlations of near infrared single photons from coherent and pseudo-thermal sources following frequency up-conversion; a study on the time-resolving measurement capability of the detectors using a short pulse pump and; evaluating the modulation of a single photon wave packet for better interfacing of independent sources. In this article, we will present an overview of the frequency up-conversion technique, introduce its applications in quantum information systems and discuss its unique features and prospects for the future.     

Cyclotron autoresonance maser with high Doppler frequency up-conversion

An LIA-unit with explosive emission injector was used as a basis for CARM with high Doppler frequency up-conversion when the wave frequency is 7 to 9 times the cyclotron frequency of electrons. Using a high-selectivity Bragg resonator as an electrodynamic system of CARM we investigated two regimes having essentially different properties: the dispersion characteristics of the electron beam and the wave either intersected or were tangential to one another. In the first case, the radiation power amounted to 50 MW at the wavelength of 4.4 mm with efficiency 8%. The efficiency significantly smaller than the design value was evidently caused by a high level of parasitic superluminiscence of the beam. In the second regime of operation at 6 mm, the radiation power was 30 MW with a low level of parasitic superluminiscence and efficiency 10% which was close to the calculated value.     

Erasing information and purity of a quantum dot via its spontaneous decay

An analytical solution to the master equation of a system describing a single quantum dot confined in a single-mode microcavity, coupled to its environment, is found. The information loss of the phase space, the purity and the relaxation process are investigated by using the Husimi distribution and its applications. It is found that the spontaneous decay leads to the loss of information of the phase space and the purity. Suggested indicator for the relaxation process is offered by using the Wehrl entropy.     

Photonic generation of millimeter-wave ultra-wideband signal using phase modulation to intensity modulation conversion and frequency up-conversion

We propose and experimentally demonstrate the generation of a pair of polarity-reversed 24 GHz millimeter-wave (MMW) ultra-wideband (UWB) monocycles. The scheme is realized by using delay interferometer (DI) based phase modulation to intensity modulation (PM–IM) conversion and carrier suppression modulation (CSM) based frequency up-conversion. The phase modulation is realized by using either electro-optic phase modulator (EOPM) or cross phase modulation (XPM) in semiconductor optical amplifier (SOA), which is an all-optical approach to obtaining baseband UWB signals, respectively. After frequency up-converted by using CSM in a Mach–Zehnder modulator (MZM), a pair of polarity-reversed 24 GHz MMW-UWB signals complying with the Federal Communication Committee (FCC) requirements is generated. The bi-phase modulation (BPM) of 24 GHz MMW-UWB signals can also be realized by electrically switching the bias voltage of delay interferometer.     

Adiabatic frequency up-conversion of a powerful electromagneticpulse producing gas ionization

The theory of strong frequency upconversion of the powerful ionizing electromagnetic radiation in gases is presented based on the modified nonlinear geometrical optics approximation. The permanent spectrum upshift versus propagation path, exceeding considerably the initial frequency, is demonstrated without strong wave dissipation for the cases of impact and field-induced ionization in the high-intensity field range. Reflectionless propagation into the supercritical plasma and broad-band tuning of the laser radiation are emphasized as highly promising physical applications of the phenomenon described     

Continuous frequency up-conversion in a double-Λ scheme of Na2

 In a double-Λ level configuration of Na₂ molecules, involving rotational–vibrational levels of the X, A and B bands, continuous resonant frequency mixing ω₄=ω₁−ω₂+ω₃ is demonstrated. A DCM dye laser at 661 nm (λ₁) pumps a molecular Raman laser at 746 nm (λ₂) in a sodium heatpipe, which is used to generate the molecular vapour. In the same heatpipe, both fields are mixed with the radiation of an argon-ion laser at 514 nm (λ₃) to generate up-converted laser radiation at 473 nm (λ₄). For laser powers of 200 mW (λ₁), 700 mW (λ₂, internal power) and 140 mW (λ₃), an output power of 120 μW (λ₄) has been achieved. Dependences of the generated radiation on the pump fields (powers and detunings) and polarization features are presented; influences of coherent coupling and population transfer mechanisms are discussed. Received: 7 October 1996     

掺E~(3+)石英光纤中频率上转换的实验研究

首次报道了实验研究连续1064nm激光泵浦的掺Er~(3+)石英光纤中频率上转换过程.测量了Er~(3+)/GeO_2/SiO_2和Er~(3+)/Al_2O_3/GeO_2/SiO_2两种光纤发射的可见荧光谱,并用Er~(3+)离子的双光子吸收和受激态吸收过程解释了频率上转换现象.     

Integration of classical communication and quantum key distribution using frequency division multiplexing

Since the working conditions of classical and quantum signals are very different, how to effectively integrate classical and quantum communication networks without affecting their respective performance has become a great challenge. In this paper, we proposed a scheme to realize classical communication and continuous-variable quantum key distribution(CVQKD) based on frequency-division multiplexing(FDM), and we verified the feasibility of simultaneously realizing CV-QKD and classical optical communication data synchronous transmission scheme under the same infrastructure. We achieved a0 bit error rate in 50 frames and a 20 Mb/s bit rate for the classical signal and an average secret key rate of around5.86 × 10～5bit/s for the quantum signal through a 4 dB fiber channel. This work provides a scheme to establish a QKD channel by only reserving a small passband in the entire optical communication instead of an entire wavelength, increasing efficiency and simplifying the integration of QKD and classical communication.     

Control of efficiency of photon energy up-conversion in CdSe/ZnS quantum dots

Efficient photoluminescence (PL) up-conversion in CdSe/ZnS quantum dots prepared by an organometallic approach is reported. It is demonstrated that the efficiency of photon energy up-conversion and the magnitude of the spectral shift can be controlled by (i) the thickness of the ZnS layers, (ii) the temperature dependence of the excited-state absorption coefficient, and (iii) the dependence on the excitation intensity. From the analysis of the experimental data, it is proposed that intrinsic gap states are involved as intermediate states in the PL up-conversion, rather than nonlinear two-photon absorption or Auger processes.     

Coherent enhancement of broadband frequency up-conversion in BBO crystal by shaping femtosecond laser pulses

An optimal feedback control of broadband frequency up-conversion in BBO crystal is experimentally demonstrated by shaping femtosecond laser pulses based on genetic algorithm, and the frequency up-conversion efficiency can be enhanced by ∼16%. SPIDER results show that the optimal laser pulses have shorter pulse-width with the little negative chirp than the original pulse with the little positive chirp. By modulating the fundamental spectral phase with periodic square distribution on SLM-256, the frequency up-conversion can be effectively controlled by the factor of about 17%. The experimental results indicate that the broadband frequency up-conversion efficiency is related to both of second harmonic generation (SHG) and sum frequency generation (SFG), where the former depends on the fundamental pulse intensity, and the latter depends on not only the fundamental pulse intensity but also the fundamental pulse spectral phase.     

Thermal stability and frequency up-conversion properties of Er3+-doped oxyfluoride tellurite glasses

The thermal properties of 68TeO2-15BaF2-5SrF2-10LaF3-2KF glass were measured by different temperature analysis (DTA). Up-conversion luminescence of Ers+ ion in the obtained glass was investigated.Mechanism of up-conversion emission was discussed. The result shows that the obtained oxyfluoride tellurite glass 68TeO2-15BaF2-5SrF2-10LaF3-2KF has a good thermal stability (△T = 153.6 ℃) and strong up-conversion green emissions around 527 nm and 549 nm and red emission at 660 nm. This glass can be a promising host material for up-conversion fiber lasers.     

Local distinguishability of multipartite unitary operations

We show that any two different unitary operations acting on an arbitrary multipartite quantum system can be perfectly distinguished by local operations and classical communication when a finite number of runs is allowed. Intuitively, this result indicates that the lost identity of a nonlocal unitary operation can be recovered locally. No entanglement between distant parties is required.