Photon Number Distribution in a Linear Directional Coupler

Abstract

The photon counting distribution of two modes in a directional coupler is studied, looking in particular at the behaviour of photon number states when losses are taken into account.     

Superposition Phases and Squeezing

Abstract

Quadrature variances of a radiation field depend not only on the photon number distribution in the field but also on the relative phases of the photon number probability amplitudes. Two fields with the same photon number distribution can show different degrees of squeezing if photon number states are superposed with different relative phases. It is thus possible, for example, for a radiation field with Poissonian photon statistics to exhibit squeezed quadrature fluctuations. Since different relative superposition phases in general yield different maximum and minimum values of the quadrature variances, measurement of the variances can yield information concerning the relative phases between different number states.     

Nonlinear quantum optical computing via measurement

Abstract

We show how the measurement induced model of quantum computation proposed by Raussendorf and Briegel (2001, Phys. Rev. Letts., 86, 5188) can be adapted to a nonlinear optical interaction. This optical implementation requires a Kerr nonlinearity, a single photon source, a single photon detector and fast feed forward. Although nondeterministic optical quantum information proposals such as that suggested by KLM (2001, Nature, 409, 46) do not require a Kerr nonlinearity they do require complex reconfigurable optical networks. The proposal in this paper has the benefit of a single static optical layout with fixed device parameters, where the algorithm is defined by the final measurement procedure.     

Photon number resolving in geiger mode avalanche photodiode photon counters

Abstract

The paper reports on research and development in the field of avalanche photodiodes operated as photon counters in a Geiger mode. A technique has been developed and tested that permits estimation of the photon number involved in a detection process. It can be applied in a time correlated photon counting experiment simultaneously with original required time interval estimation. A time walk compensation circuit provides uniform electrical pulses, and the time interval between them is related to the number of photons detected. Employing a picosecond event timing device, the photon number can be estimated within the dynamic range 1–1000 photons with resolution better than a factor of three.     

Towards photostatistics from photon-number discriminating detectors

Abstract

We study the properties of a photodetector that has a numberresolving capability. In the absence of dark counts, due to its finite quantum efficiency, photodetection with such a detector can only eliminate the possibility that the incident field corresponds to a number of photons less than the detected photon number. We show that such a non-photon number-discriminating detector, however, provides a useful tool in the reconstruction of the photon number distribution of the incident field even in the presence of dark counts.     

Recent progress on cooled avalanche photodiodes for single photon detection

Abstract

Recent results on the properties of cooled avalanche photodiodes for single photon detection are presented. Results from Hamamatsu silicon photodiodes, originally developed as radiation-hard photodetectors for high energy physics experiments, are extremely encouraging. Gains of approximately 10,000 can be achieved with the APD operating in proportional mode. Together with a low noise amplifier they allow photon counting with extremely high efficiency and very low noise making cold APDs almost ideal single photon detectors. Operation of APDs in Geiger mode is also reported, together with measurements of detection efficiency and noise as function of operating voltage. Prospects and hopes for future work are briefly summarized.     

Single photon counting at telecom wavelength and quantum key distribution

Abstract

A brief overview is given of single photon detector performance requirements for quantum cryptography applications. The analysis is made with respect to restrictions necessary to secure the quantum key distribution channel. InGaAs/InP avalanche photodiode performance is analysed for single photon counting at 1550 nm. Quantum efficiency, dark current and afterpulsing probability (for times up to 100μs after an initial avalanche) are studied in a wider temperature range than previously reported (0deg; C to –80deg;C). We show that photon counting is a bottle-neck in current quantum key distribution systems and provides the source for future performance improvement.     

Photon Statistics of Atomic Fluorescence Near a Phase-conjugate Mirror or a Degenerate Parametric Amplifier

Abstract

We have studied the modification of the photon statistics of the resonance fluorescence of a coherently driven two-state atom due to the presence of a phase-conjugate mirror (PCM) or a degenerate parametric amplifier (DPA). In both cases, we give explicit expressions for the n-fold intensity correlation function. We find that the photon statistics depends on the relative phase of the PCM or DPA and the driving field. The non-classical properties of the photon statistics can be enhanced because of the presence of the PCM or of the DPA, when the decay of the coherences is obstructed.     

Influence of Resqueezing on Nonclassical Photon Statistics

Abstract

The nonclassical photon statistics of one-mode and two-mode combination squeezed states introduced recently by Fan, which have less fluctuation in one quadrature phase than the usual two-mode squeezed states, is discussed. It is found that increasing the degree of two-mode squeezing cannot always increase the photon antibunching depth of these generalized two-mode squeezed states.     

Adiabatic state preparation in a cavity

Abstract

The paper discusses the single-mode Jaynes-Cummings model with time-dependent parameters. Solvable models for two-level systems are utilized to consider the changes in the photon distribution effected by the passage of atoms through the cavity. It is suggested that such systems may be used as filters to modify the photon distribution. The effect can be enhanced by repeatedly sending new atoms through the cavity. We show that such filters can cut out either small or large photon numbers. It is also shown that the method can be used to narrow down photon distributions and in this way achieve highly non-classical sub-Poissonian states. Some limitations and applications of the method are presented.     

Statistical Properties of a New Squeezed Operator Model

Abstract

We introduce a new squeezed operator which is a combination of the two-mode squeezed operator and the two single photon squeezed operator. Here we study the effects of this operator on the photon number sum and difference. The squeezing in the frequency converter model has been examined, and statistical investigations are carried out for the quasi-probability distribution functions (Wigner function and Q-function). An application to the parametric amplifier is given.     

Accuracy of sampling quantum phase space in a photon counting experiment

Abstract

We study the accuracy of determining the phase space quasi-distribution of a single quantized light mode by a photon counting experiment. We derive an exact analytical formula for the error of the experimental outcome. This result provides an estimate of the experimental parameters, such as the number of events, required to determine the quasi-distribution with assumed precision. Our analysis also shows that it is, in general, not possible to compensate for the imperfection of the photodetector in the numerical processing of the experimental data. The discussion is illustrated with Monte Carlo simulations of the photon counting experiment for the coherent state, the one photon Fock state, and the Schrödinger cat state.     

Study of Photon Antibunching in the Vacuum Field Two-photon Jaynes-Cummings Model Without the Rotating-wave Approximation

Abstract

We have numerically investigated photon antibunching in the two-photon Jaynes-Cummings model without the rotating-wave approximation when the system is restricted to the following initial condition: the atom in the excited state and the field in the vacuum state. The influence of the detuning Δ on photon antibunching has also been discussed.     

Spectral and Temporal Distribution of Phase-conjugated Fluorescent Photons

Abstract

Spontaneous emission of fluorescence radiation by an atom near the surface of a four-wave mixing phase conjugator is considered. It is shown that the spectral photon distribution consists of two Lorentzians, which have their peaks symmetrically located at the two sides of the pump frequency ¯ω of the nonlinear crystal. With ω₀ the atomic resonance, the line at 2¯ω?ω₀ is more than twice as strong as the line at ω₀. When the phase-conjugate reflectivity exceeds unity, the temporal photon distribution exhibits nonclassical behaviour. Then, antibunching of photons prevails, and the photon statistics are sub-Poissonian.     

Determining the state of a single cavity mode from photon statistics

Abstract

We present various schemes for measuring the quantum state of a single mode of the electromagnetic field. These involve measuring the photon statistics for the mode before and after an interaction with either one or two two-level atoms. The photon statistics conditioned on the final state of the atoms, for two choices of the initial set of atomic states, along with the initial photon statistics, may be used to calculate the complete quantum state in a simple manner. Alternatively, when one atom is used, two unconditioned sets of photon statistics, each after interaction with a single atom in different initial states, along with the initial photon statistics may be used to calculate the initial state in a simple manner. When the cavity is allowed to interact with just one atom, only pure cavity states which do not contain zeros in the photon distribution may be reconstructed. When two atoms are used we may reconstruct pure states which do not contain adjacent zeros in the photon distribution. Coherent states and number states are among those that may be measured with one-atom interaction, and squeezed states and ?Schrödinger cats‘ are among those that may be measured with a two-atom interaction.     

Quantum limits on pixel resolution from non-commutative photon coordinates

Abstract

Non-commutative geometry sets lower bounds on pixel resolution in photon detector technology.     

Cavity-enhanced parametric down-conversion as a source of correlated photons

Abstract

The most common way of generating correlated photons is by parametric down-conversion in a nonlinear crystal in free space. However, a drawback of this technique is the extremely low photon flux available. We present a simple analysis which shows that cavity-enhanced parametric downconversion, using an arrangement similar to an optical parametric oscillator and operated well below threshold, can yield a substantially higher photon flux without significantly degrading the correlation between photons.     

High efficiency single photon detection via frequency up-conversion

Abstract

We propose a method of single photon detection of infrared (IR) photons at potentially higher efficiencies and lower noise than allowed by traditional IR band avalanche photodiodes (APDs). By up-converting the photon from the IR, e.g. 1550 nm, to a visible wavelength in a nonlinear crystal, we can utilize the much higher efficiency of silicon APDs at these wavelengths. We have used a periodically poled lithium niobate (PPLN) crystal and a pulsed 1064 nm Nd:YAG laser to perform the up-conversion to a 631 nm photon. We observed conversion efficiencies as high as ～ 80%, and demonstrated scaling down to the single photon level while maintaining a background of 3 ×s; 10^?4 dark counts per count. We also propose a 2-crystal extension of this scheme, whereby orthogonal polarizations may be up-converted coherently, thus enabling complete quantum state transduction of arbitrary states.     

Study of Induced Temporal Coherence in Optical Parametric Down Conversion

Abstract

Temporal coherence of the idler photon beam induced by a coherent input signal was studied for non-degenerate optical parametric down conversion. When the optical path difference of the interferometer is much longer than the coherence length of the spontaneous idler radiation, the experimental results show that the first-order temporal coherence of the idler photon can be induced by a coherence input signal and the interference fringe visibility is determined by the intensity of the coherent input signal.