Transform-Limited-Pulse Representation of Excitation with Natural Incoherent Light

We study the natural excitation of molecular systems, applicable to, for example, photosynthetic light-harvesting complexes, by natural incoherent light. In contrast with the conventional classical models, we show that the light need not have random character to properly represent the resultant linear excitation. Rather, thermal excitation can be interpreted as a collection of individual events resulting from the system's interaction with individual, deterministic pulsed realizations that constitute the field. The derived expressions for the individual field realizations and excitation events allow for a wave function formalism, and therefore constitute a useful calculational tool to study dynamics following thermal-light excitation. Further, they provide a route to the experimental determination of natural incoherent excitation using pulsed laser techniques.Comment: 5 pages, 3 figures, 1 page supplementary information. Comments welcom

Nonclassicality of a photon-subtracted Gaussian field

Published versio

Quantum Bayesian methods and subsequent measurements

After a derivation of the quantum Bayes theorem, and a discussion of the reconstruction of the unknown state of identical spin systems by repeated measurements, the main part of this paper treats the problem of determining the unknown phase difference of two coherent sources by photon measurements. While the approach of this paper is based on computing correlations of actual measurements (photon detections), it is possible to derive indirectly a probability distribution for the phase difference. In this approach, the quantum phase is not an observable, but a parameter of an unknown quantum state. Photon measurements determine a probability distribution for the phase difference. The approach used in this paper takes into account both photon statistics and the finite efficiency of the detectors.Comment: Expanded and corrected version. 13 pages, 1 figur

Quantum random walk of two photons in separable and entangled state

We discuss quantum random walk of two photons using linear optical elements. We analyze the quantum random walk using photons in a variety of quantum states including entangled states. We find that for photons initially in separable Fock states, the final state is entangled. For polarization entangled photons produced by type II downconverter, we calculate the joint probability of detecting two photons at a given site. We show the remarkable dependence of the two photon detection probability on the quantum nature of the state. In order to understand the quantum random walk, we present exact analytical results for small number of steps like five. We present in details numerical results for a number of cases and supplement the numerical results with asymptotic analytical results

Directory of aerospace safety specialized information sources

Directory aids safety specialists in locating information sources and individual experts in engineering-related fields. Lists 170 organizations and approximately 300 individuals who can provide safety-related technical information in form of documentation, data, and consulting expertise. Information on hazard and failure cause identification, accident analysis, and materials characteristics are covered

Cavity quantum electro-optics. II. Input-output relations between traveling optical and microwave fields

In the previous paper [M. Tsang, Phys. Rev. A 81, 063837 (2010), e-print arXiv:1003.0116], I proposed a quantum model of a cavity electro-optic modulator, which can coherently couple an optical cavity mode to a microwave resonator mode and enable novel quantum operations on the two modes, including laser cooling of the microwave mode, electro-optic entanglement, and backaction-evading optical measurement of a microwave quadrature. In this sequel, I focus on the quantum input-output relations between traveling optical and microwave fields coupled to a cavity electro-optic modulator. With red-sideband optical pumping, the relations are shown to resemble those of a beam splitter for the traveling fields, so that in the ideal case of zero parasitic loss and critical coupling, microwave photons can be coherently up-converted to "flying" optical photons with unit efficiency, and vice versa. With blue-sideband pumping, the modulator acts as a nondegenerate parametric amplifier, which can generate two-mode squeezing and hybrid entangled photon pairs at optical and microwave frequencies. These fundamental operations provide a potential bridge between circuit quantum electrodynamics and quantum optics.Comment: 12 pages, 10 figures, v2: updated and submitte

Microwave Photon Detector in Circuit QED

Quantum optical photodetection has occupied a central role in understanding radiation-matter interactions. It has also contributed to the development of atomic physics and quantum optics, including applications to metrology, spectroscopy, and quantum information processing. The quantum microwave regime, originally explored using cavities and atoms, is seeing a novel boost with the generation of nonclassical propagating fields in circuit quantum electrodynamics (QED). This promising field, involving potential developments in quantum information with microwave photons, suffers from the absence of photodetectors. Here, we design a metamaterial composed of discrete superconducting elements that implements a high-efficiency microwave photon detector. Our design consists of a microwave guide coupled to an array of metastable quantum circuits, whose internal states are irreversibly changed due to the absorption of photons. This proposal can be widely applied to different physical systems and can be generalized to implement a microwave photon counter.Comment: accepted in Phys. Rev. Let

Fluctuations in the formation time of ultracold dimers from fermionic atoms

We investigate the temporal fluctuations characteristic of the formation of molecular dimers from ultracold fermionic atoms via Raman photoassociation. The quantum fluctuations inherent to the initial atomic state result in large fluctuations in the passage time from atoms to molecules. Assuming degeneracy of kinetic energies of atoms in the strong coupling limit we find that a heuristic classical stochastic model yields qualitative agreement with the full quantum treatment in the initial stages of the dynamics. We also show that in contrast to the association of atoms into dimers, the reverse process of dissociation from a condensate of bosonic dimers exhibits little passage time fluctuations. Finally we explore effects due to the non-degeneracy of atomic kinetic energies.Comment: 7 pages, 6 figure

Quantum Non-Demolition Test of Bipartite Complementarity

We present a quantum circuit that implements a non-demolition measurement of complementary single- and bi-partite properties of a two-qubit system: entanglement and single-partite visibility and predictability. The system must be in a pure state with real coefficients in the computational basis, which allows a direct operational interpretation of those properties. The circuit can be realized in many systems of interest to quantum information.Comment: 4 pages, 2 figure

Quantum state transfer via temporal kicking of information

We propose a strategy for perfect state transfer in spin chains based on the use of an unmodulated coupling Hamiltonian whose coefficients are explicitly time dependent. We show that, if specific and non-demanding conditions are satisfied by the temporal behavior of the coupling strengths, our model allows perfect state transfer. The paradigma put forward by our proposal holds the promises to set an alternative standard to the use of clever encoding and coupling-strength engineering for perfect state transfer.Comment: 7 pages, 7 figures, RevTeX