Ghost imaging and ghost interference with pseudo-thermal light: Mode-separation by pure software processing

We report on a new experiment in which ghost imaging and ghost interference with quasi-thermal light are simultaneously obtained from the same set of experimental reference patterns. By sliding the mask along the object arm in a continuous way, one can see imaging and diffraction patterns to come to light and fade out in opposite directions.     

A degenerate three-level laser with a parametric amplifier

The aim of this paper is to study the squeezing and statistical properties of the light produced by a degenerate three-level laser whose cavity contains a degenerate parametric amplifier. In this quantum optical system the top and bottom levels of the three-level atoms injected into the laser cavity are coupled by the pump mode emerging from the parametric amplifier. For a linear gain coefficient of 100 and for a cavity damping constant of 0.8, the maximum intracavity squeezing is found at steady state and at threshold to be 93%.     

Degenerate three-level cascade laser with the cavity mode driven by coherent light

We present the quantum statistical properties of the light produced by a degenerate three-level cascade laser with the cavity mode driven by coherent light. In this system three-level atoms in a cascade configuration, initially prepared in a coherent superposition of the top and bottom levels, are injected into a cavity coupled a vacuum reservoir. We find that although the driving coherent light has no effect on the degree of squeezing, it increases the mean photon number considerably. Therefore, this quantum optical system can be taken as a source of a bright squeezed light.     

Analysis on generation schemes of Schrödinger cat-like states under experimental imperfections

An analysis and a comparison of two generation schemes of Schrödinger cat-like state including experimental imperfections are presented. Under practical conditions, a scheme using a squeezed vacuum and a photon subtraction will generate a cat-like state with its fidelity to the Schrödinger cat state F = 0.815 and value of its Wigner function at the origin of the phase space W(0,0) = −0.203, and then turned out to be more feasible than the scheme using squeezed single-photon state. The non-classicality of these cat-like states is governed only by non-classical photon number statistics. The criteria for ensuring W(0,0) < 0 are also presented in terms of imperfection parameter diagrams.     

Generation of pair coherent state using weak cross-Kerr media

We firstly give a nonlocal method for generating pair coherent state with two traveling wave fields in distinct districts. The experimental scheme proposed is based on a two-mode photon number matching process, which employs weak cross-Kerr media and on/off detection. Then we discuss the details for implementing this scheme, showing that it is robust against the low quantum efficiency of photon detectors and offers nearly perfect pair coherent states. Finally, we show how a two-mode Schrödinger cat state and a generalized two-mode correlated photon number state can be prepared via this matching process.     

Ghost diffraction, lensless system and 2-f system

We investigate two imaging schemes, lensless system and 2-f system which are used to implement ghost diffraction. It is shown that the two schemes have similar intensity fluctuation correlation functions which both realize the function of the Fourier-transform imaging, and the diffraction pattern is in agreement with that in the classical wave optics. The difference of the imaging visibility in the two systems is also discussed.     

Unsolved problems in quantum optics (several short notes)

The possible prospects for the improvement of the resolution and of the sensitivity in quantum-optics experiments are discussed as well as possible applications of quantum-optics methods for the solution of fundamental physical problems.Dedicated to H. Walther on the ocassion of his 60th birthday     

Enhanced squeezing and entanglement in a non-degenerate three-level cascade laser with injected squeezed light

We consider a non-degenerate three-level cascade laser coupled to a two-mode squeezed vacuum reservoir via the lossy single-port mirror. Applying the pertinent master equation, we analyze the effects of the injected squeezed light on the quadrature squeezing, entanglement and normalized intensity difference fluctuations. We show that the injected squeezed light considerably enhances the degree of squeezing and entanglement in the two-mode light for certain initial conditions. Moreover, the injected squeezed light increases the mean photon number where the squeezing and entanglement is significant. We also show that the presence of the injected squeezed light greatly reduces the noise in the intensity difference.     

Effects on squeezing and sub-poissonian of light in fourth harmonic generation up to first-order Hamiltonian interaction

The effects on squeezing and sub-poissonian of light in fourth harmonic generation (FHG) are investigated based on the fully quantum mechanically up to the first order Hamiltonian interaction in gt, where g is the coupling constant between the modes per second and t is the interaction time between the waves during the process in a nonlinear medium. FHG is a process in which an incident laser beam of the fundamental frequency ω interacts with a nonlinear medium to produce the harmonic frequency at 4ω. The coupled Heisenberg equations of motion involving real and imaginary parts of the quadrature operators are established. The occurrence of amplitude squeezing effects in both the quadratures of the radiation field in the fundamental mode is investigated and found to be dependent on the selective phase values of the field amplitude. The photon statistics of the pump mode in this process have also been investigated and found to be sub-poissonian in nature. It is found that there is no possibility to produce squeezed light in the harmonic mode up to first-order interaction in gt. Further, we have found the case up to second-order Hamiltonian interaction in gt that the normal squeezing in the harmonic mode is directly depends upon the fourth-order squeezing of the initial pump field. This gives a method of converting higher-order (fourth-order) squeezing into normal squeezing in the harmonic mode and vice versa.     

Experimental Study on Practical Quantum Key Distribution Scheme with Time-Multiplexed Technique

We present a scheme that is capable of detecting photon numbers during the quantum key distribution (QKD) based on an improved differential phase shift (DPS) system without Trojan horse attack. A time-multiplexed detector (TMD) is set in for the photon-number resolution. Two fibre loops are used for detecting photon numbers as well as distributing keys. The long-term stabilization is guaranteed by two Faraday mirrors (FM) at Bob's site to automatically compensate for polarization defect. Our experimental study (90km QKD is completed) indicates that such a system is stable and secure which nearly reaches the performance of a single photon scheme.     

Interaction of a two-level atom with squeezed light

We consider a degenerate parametric oscillator whose cavity contains a two-level atom. Applying the Heisenberg and quantum Langevin equations, we calculate in the bad-cavity limit the mean photon number, the quadrature variance, and the power spectrum for the cavity mode in general and for the signal light and fluorescent light in particular. We also obtain the normalized second-order correlation function for the fluorescent light. We find that the presence of the two-level atom leads to a decrease in the degree of squeezing of the signal light. It so turns out that the fluorescent light is in a squeezed state and the power spectrum consists of a single peak only.     

Quantum correlated twin beams

We discuss recent progress in the study of the non-classical properties of light beams generated by non-degenerate parametric splitting in ⁽²⁾ nonlinear birefringent crystals, with special emphasis on their quantum correlation (twin beams). We describe experimental results using successively pure parametric fluorescence, parametric amplification of a weak signal beam pumped by a pulsed laser, and parametric oscillation in a cavity pumped by a cw laser. In this review, we compare the respective advantages and drawbacks of the different approaches.     

Nonclassical state via superposition of two coherent states (π/2 out of phase) and related entangled states

Nonclassical features of the superposition of two coherent states which are π/2 out of phase are discussed, such as sub-Poissonian photon statistics and quadrature squeezing, as well as negativity of the Wigner function. Special nonclassicality is found in the special state where the relative phase of superposition has relationship with the average photon number. The analysis of the amount of entanglement is also presented for the related two-mode entangled coherent states.     

On a heuristic point of view related to quantum nonequilibrium statistical mechanics

In this paper I propose a new way for counting the microstates of a system out of equilibrium. As, according to quantum mechanics, things happen as if a given particle can be found in more than one state at once, I extend this concept to propose the coherent access by a particle to the available states of a system. By coherent access I mean the possibility for the particle to act as if it is populating more than one microstate at once. This hypothesis has experimental implications, since the thermodynamical probability and, as a consequence, the Bose-Einstein distribution as well as the argument of the Boltzmann factor is modified.     

Improving Visibility of Diffraction Pattern with Pseudo-Thermal Light

We report an experimental observation of Poisson＇s spot with pseudo-thermal light. The experimental results show that the diffraction pattern disappears in the intensity distribution behind the opaque disc but emerges through both auto-correlation and cross-correlation intensity measurements. The auto-correlation scheme can take care of both better visibility and higher resolution of the diffraction pattern under the condition that the thermal light source has a larger spectral bandwidth.     

Interference from nonlocal double-slit with pseudo-thermal light

We perform an interference experiment in which a pseudo-thermal light beam illuminates two spatially separated apertures, whose superposition at the same place forms a double-slit. The experimental result exhibits a typical double-slit interference fringe in the intensity correlation measurement, in agreement with the theoretical analysis by means of the property of the second-order spatial correlation of field of the thermal light.     

Bright entangled light from two-mode cascade laser

We show that a two-mode three-level cascade laser driven by external coherent fields generate intense entangled light. It turns out that external driving fields which are at resonance with the cavity modes substantially improve the intensity of the two-mode light in the cavity in a region where the squeezing and entanglement is significant making the system under consideration a viable source of bright squeezed as well as entangled light.     

Scheme for Direct Measurement of the Wigner Function via Resonant Interaction

We propose a scheme for direct measurement of the Wigner function for a cavity mode. In the scheme the cavity field resonantly interacts with an atomic ensemble. Under certain conditions, the state of the cavity mode is transferred to the atomic system. After a displacement the measurement of the parity of the atomic excitation number directly yields the Wigner function of the initial state of the cavity mode.     

Reduction of quantum phase fluctuations in intermediate states

Recently we have shown that the reduction of the Carruthers-Nieto symmetric quantum phase fluctuation parameter (U) with respect to its coherent state value corresponds to an antibunched state, but the converse is not true. Consequently reduction of U is a stronger criterion of nonclassicality than the lowest order antibunching. Here we have studied the possibilities of reduction of U in intermediate states by using the Barnett-Pegg formalism. We have shown that the reduction of phase fluctuation parameter U can be seen in different intermediate states, such as binomial state, generalized binomial state, hypergeometric state, negative binomial state, and photon added coherent state. It is also shown that the depth of nonclassicality can be controlled by various parameters related to intermediate states. Further, we have provided specific examples of antibunched states, for which U is greater than its Poissonian state value.