Time reversal in matter-wave optics

The evolution of atomic wave packets experiencing so-called comoving potential pulses is examined theoretically, in the framework of the stationary-phase approximation. The negative refraction induced by this potential is a characteristic property of negative-index media, the atomic counterpart of negative-index materials of light optics. A novel process, specific of negative-index for matter waves, is evidenced, namely a narrowing of the wave packet transiently counterbalancing the natural spreading. This is the manifestation of a general property of negative-index media, i.e. a time reversal effect. It is shown that, for a statistical ensemble of wave packets leading to a moderate dispersion of the times of flight, this time reversal phenomenon should be observable.     

Squeezed-state purification with linear optics and feedforward

A scheme for optimal and deterministic linear optical purification of mixed squeezed Gaussian states is proposed and experimentally demonstrated. The scheme requires only linear optical elements and homodyne detectors, and allows the balance between purification efficacy and squeezing degradation to be controlled. One particular choice of parameters gave a tenfold reduction of the thermal noise with a corresponding squeezing degradation of only 11%. We prove optimality of the protocol, and show that it can be used to enhance the performance of quantum informational protocols such as dense coding and entanglement generation.     

Nonlinear optics with stationary pulses of light

We show that the recently demonstrated technique for generating stationary pulses of light [M. Bajcsy, A. S. Zibrov, and M. D. Lukin, Nature (London) 426, 638 (2003)] can be extended to localize optical pulses in all three spatial dimensions in a resonant atomic medium. This method can be used to dramatically enhance the nonlinear interaction between weak optical pulses. In particular, we show that an efficient Kerr-like interaction between two pulses can be implemented as a sequence of several purely linear optical processes. The resulting process may enable coherent interactions between single photon pulses.     

Time reversal symmetry in light scattering by excitations in a film

We present a general symmetry argument for light scattering by excitations in an insulator film. The analysis holds for bulk continuum, guided and surface excitations.The main results represent a simplification of the theory and a better understanding for the time reversal properties of the system. Those properties hold both for forward and backward scatering, and are independent of the substrate upon which the film is deposited. We show that the asymmetry in the shape of the cross-section which is common to many experimental situations is in fact a consequence of the time reversal properties of the system.     

Fast multi-copy entanglement purification with linear optics

We describe an entanglement purification protocol for a polarization Bell state. Different from the previous protocols,it does not require the controlled-not gate, and only uses linear optical elements to complete the task. This protocol requires multi-copy degraded mixed states, which can make this protocol obtain a high fidelity in one purification step. It can also be extended to purify the multi-photon Greenberger–Horne–Zeilinger(GHZ) state. This protocol may be useful in future long-distance communication.     

Passive quantum error correction with linear optics

Recently it was proposed by Kalamidas in [D. Kalamidas, Phys. Lett. A 343 (2005) 331] an optical set-up able to correct single qubit errors using Pockels cells. In this work, we present a different set-up able to realize error correction passively, in the sense that none external action is needed.     

Optical processing with twin ultrasonic light modulators

A collinear optical heterodyne system with twin ultrasonic light modulators (ULM) is considered within the Raman-Nath regime. The zeroth order beam of light emerging from the first ULM enters the second ULM and splits into the diffraction spectrum with the frequencies shifted by integral multiples of the driving sound frequency. For the purpose of photomixing, the positive or negative first order beam in this spectrum can be superposed on the first order beam of light from the first ULM which passes through the second ULM without deflection, and comes to the same location as the other. Experimental verification is successfully carried out by producing a beat signal of light with a difference frequency between two sound frequencies. It is demonstrated analytically that a convolution or correlation function between two time varying signals can be obtained, according to whether the beat signal of light has the sum or difference frequency of the two driving sound frequencies. The sum or difference frequency can be generated as one of the sound waves proceeds in the same or reverse direction as the other.     

Time reversal during magnetization of gas atoms by a resonant light pulse

The optically induced magnetic moment of a stationary atom is calculated as a function of time and the resonance detuning ω-ω _ba to within a constant factor having the dimensions of a magnetic moment based on the symmetry of an atom in the field of a resonant light pulse and symmetry with respect to time reversal including the initial conditions. The even dependence of the optically induced magnetic moment on ω-ω _ba for an elliptically polarized pulse with an isotropic initial state of the atom and its odd dependence on ω-ω _ba in the case of a linearly polarized pulsed with an anisotropic initial state in the atom’s alignment are shown to be consequences of symmetry with respect to time reversal and the initial conditions. This behavior is retained even after passage of the light pulse, when the resulting relaxation destroys the time reversal symmetry. The optically induced magnetization of an atomic gas is found to have analogous properties. Zh. éksp. Teor. Fiz. 112, 453–469 (August 1997)     

Optically-addressed spatial light modulators

The performance characteristics of three unique optically-addressed spatial light modulators (SLMs) have been experimentally investigated. The measured parameters include resolution, visibility, imaging response time, and write light sensitivity. The modulators investigated include two relatively new technologies, the ferroelectric liquid crystal (FLC) SLM from the University of Colorado-Boulder and the amorphous silicon photoconductive twisted nematic liquid crystal SLM from GEC-Marconi Research, and a well-established industry benchmark, the Hughes Liquid Crystal Light Valve (LCLV).     

Single-photon quantum error rejection and correction with linear optics

We present single-photon schemes for quantum error rejection and correction with linear optics. In stark contrast with other known proposals, our schemes do not require multi-photon entangled states, are not probabilistic, and their application is not restricted to single bit-flip errors.     

One-step deterministic multipartite entanglement purification with linear optics

We present a one-step deterministic multipartite entanglement purification scheme for an N-photon system in a Greenberger-Horne-Zeilinger state with linear optical elements. The parties in quantum communication can in principle obtain a maximally entangled state from each N-photon system with a success probability of 100%. That is, it does not consume the less-entangled photon systems largely, which is far different from other multipartite entanglement purification schemes. This feature maybe make this scheme more feasible in practical applications.     

Time reversal and object reconstruction with single-cycle pulses

We demonstrate the reconstruction of one- and two-dimensional objects by numerically backpropagating measured scattered terahertz transients. The spatial resolution determined by the Sparrow criterion is found to correspond to approximately 30% of the peak wavelength and 85% of the mean wavelength of the power spectrum of the single-cycle waveform.     

Driving power for light modulators with interdigital electrodes

Surface field distribution induced inside an electro-optic crystal by a set of interdigital electrodes are examined more rigorously than in a previous paper about surface field electro-optic light modulators. Capacitance, effective modulating voltage, and required driving power for the modulator are calculated as a function of a structural parameter that is the ratio of the spacing to the width of electrode strips. The results are compared with the experimental values.     

Near field optics and light confinement

By exploring the surface of an illuminated object at a very short distance by means of a subwavelength detector, it is possible to reconstruct images whose resolution is beyond the diffraction limit. This opportunity due to the properties of near fields can be explained in terms of non radiating field detection. Such a detection is the basis of near field microscopy. In this communication emphasis will be put on some fundamental aspects of the new concept of non radiative optics such as the relation between Rayleigh criterion and Heisenberg principle and the notion of light confinement. Some proposals of non radiative transfers will be evoked.     

Near-deterministic discrimination of all Bell states with linear optics

For a reliable implementation of quantum teleportation, a near-deterministic (close to 100%) discrimination of all four Bell states of entangled qubits is required. One can carry it out with linear optical elements only if conditional dynamics are allowed. Here we present a setup in which we repeatedly disentangle and reentangle photons in three of four states, so as to separate photons in one of them, conditioned on keeping the other two at bay. The efficiency of a realistic implementation of our setup with current technology is over 90% for an ideal source of photons on demand.     

Optimizing linear optics quantum gates

In this Letter, the problem of finding optimal success probabilities of linear optics quantum gates is linked to the theory of convex optimization. It is shown that by exploiting this link, upper bounds for the success probability of networks realizing single-mode gates can be derived, which hold in generality for postselected networks of arbitrary size, any number of auxiliary modes, and arbitrary photon numbers. As a corollary, the previously formulated conjecture is proven that the optimal success probability of a nonlinear sign shift without feedforward is 1/4, a gate playing the central role in the scheme of Knill-Laflamme-Milburn for quantum computation. The concept of Lagrange duality is shown to be applicable to provide rigorous proofs for such bounds, although the original problem is a difficult nonconvex problem in infinitely many objective variables. The versatility of this approach is demonstrated.     

Time reversal and exceptional points

Eigenvectors of decaying quantum systems are studied at exceptional points of the Hamiltonian. Special attention is paid to the properties of the system under time reversal symmetry breaking. At the exceptional point the chiral character of the system -- found for time reversal symmetry -- generically persists. It is, however, no longer circular but rather elliptic.Received: 20 November 2003, Published online: 15 April 2004PACS: 03.65.Vf Phases: geometric; dynamic or topological - 02.30.-f Function theory, analysis - 05.45.Mt Quantum chaos; semiclassical methods     

Time reversal and the neutron

We have measured the triple correlation $D\langle\vec J_n\rangle/J_n\cdot (\vec\beta_e\times\hat p_\nu)$ with a polarized cold-neutron beam (Mumm et al., Phys Rev Lett 107:102301, 2011; Chupp et al., Phys Rev C 86:035505, 2012). A non-zero value of D can arise due to parity-even-time-reversal-odd interactions that imply CP violation. Final-state effects also contribute to D at the level of 10^???5 and can be calculated with precision of 1 % or better. The D coefficient is uniquely sensitive to the imaginary part of the ratio of axial-vector and vector beta-decay amplitudes as well as to scalar and tensor interactions that could arise due to beyond-Standard-Model physics. Over 300 million proton-electron coincidence events were used in a blind analysis with the result D?=?[???0.94±1.89 (stat)±0.97(sys)]×10^???4. Assuming only vector and axial vector interactions in beta decay, our result can be interpreted as a measure of the phase of the axial-vector coupling relative to the vector coupling, $\phi_{\rm AV}= 180.012^\circ \pm 0.028^\circ$ . This result also improves constrains on certain non-VA interactions.     

Time reversal for systems with internal symmetry

Wigner time reversal implemented by antiunitary transformations on the wavefunctions is to be refined if we are to deal with systems with internal symmetry. The necessary refinements are formulated. Application to a number of physical problems is made with some unexpected revelations about some popular models.This paper is presented in felicitation of Jean-Pierre Vigier with pleasant recollections of his infectious enthusiasm. This work is supported in part by DOE Grant No. DE-FG03-93ER40757. The authors thank Iwo Bialynicki-Birula and J. Bruce French for sharing their insights, and Luis J. Boya for discussions.