Anatoly A. Svidzinsky

Quantum heat engine power can be increased by noise-induced coherence

Laser and photocell quantum heat engines (QHEs) are powered by thermal light and governed by the laws of quantum thermodynamics. To appreciate the deep connection between quantum mechanics and thermodynamics we need only recall that in 1901 Planck introduced the quantum of action to calculate the entropy of thermal light, and in 1905 Einstein’s studies of the entropy of thermal light led him to introduce the photon. Then in 1917, he discovered stimulated emission by using detailed balance arguments. Half a century later, Scovil and Schulz-DuBois applied detailed balance ideas to show that maser photons were produced with Carnot quantum efficiency (see Fig. 1A). Furthermore, Shockley and Quiesser invoked detailed balance to obtain the efficiency of a photocell illuminated by “hot” thermal light (see Fig. 2A). To understand this detailed balance limit, we note that in the QHE, the incident light excites electrons, which can then deliver useful work to a load. However, the efficiency is limited by radiative recombination in which the excited electrons are returned to the ground state. But it has been proven that radiatively induced quantum coherence can break detailed balance and yield lasing without inversion. Here we show that noise-induced coherence enables us to break detailed balance and get more power out of a laser or photocell QHE. Surprisingly, this coherence can be induced by the same noisy (thermal) emission and absorption processes that drive the QHE (see Fig. 3A). Furthermore, this noise-induced coherence can be robust against environmental decoherence.Fig. 1. (A) Schematic of a laser pumped by hot photons at temperature Th (energy source, blue) and by cold photons at temperature Tc (entropy sink, red). The laser emits photons (green) such that at threshold the laser photon energy and pump photon energy is related by Carnot efficiency (4). (B) Schematic of atoms inside the cavity. Lower level b is coupled to the excited states a and β. The laser power is governed by the average number of hot and cold thermal photons, and

The Super of Superradiance

Cooperative single-photon emission from an atom ensemble will provide insights into quantum electrodynamics and applications in quantum communication. In 1954, Robert Dicke introduced the concept of superradiance in describing the cooperative, spontaneous emission of photons from a collection of atoms. The concept of superradiance can be understood by picturing each atom as a tiny antenna emitting electromagnetic waves. Thermally excited atoms emit light randomly, and the emitted intensity is a function of the number of atoms, N. However, when the atomic “antennas” are coherently radiating in phase with each other, the net electromagnetic field is proportional to N, and therefore, the emitted intensity goes as N2. As a result, the atoms radiate their energy N times faster than for incoherent emission. It is this anomalous radiance that Dicke dubbed “superradiance” (1–3).

Dynamical evolution of correlated spontaneous emission of a single photon from a uniformly excited cloud of N atoms.

We study the correlated spontaneous emission from a dense spherical cloud of N atoms uniformly excited by absorption of a single photon. We find that the decay of such a state depends on the relation between an effective Rabi frequency Omega proportional square root N and the time of photon flight through the cloud R/c. If OmegaR/c<1 the state exponentially decays with rate Omega(2)R/c and the state lifetime is greater than R/c. In the opposite limit OmegaR/c>>1, the coupled atom-radiation system oscillates between the collective Dicke state (with no photons) and the atomic ground state (with one photon) with frequency Omega while decaying at a rate c/R.

Quasiparticle bound states and low-temperature peaks of the conductance of NIS junctions in d-wave superconductors

Contributions of quasiparticle states, bound to the boundary of anisotropically paired superconductors, to the density of states and to the conductance of normal-metal{endash}insulator{endash}superconduction (NIS) junctions are studied both analytically and numerically. For smooth surfaces and real order parameters, we find some general results for the bound-state energies. In particular, we show that under fairly general conditions quasiparticle states with nonzero energies exist for momentum directions within a narrow region around the surface normal. The energy dispersion of the bound states always has an extremum for the direction along the normal. Along with the zero-bias anomaly due to midgap states, we find, for quasi-two-dimensional materials, additional low-temperature peaks in the conductance of NIS junctions for voltages determined by the extrema of the bound-state energies. The influence of interface roughness on the conductance is investigated within the framework of Ovchinnikov{close_quote}s model. We show that nonzero-bias peaks at low temperatures may give information on the order parameter in the bulk, even though it is suppressed at the surface. {copyright} {ital 1997} {ital The American Physical Society}

Cooperative spontaneous emission as a many-body eigenvalue problem

We study emission of a single photon from a spherically symmetric cloud of

Anomalous Modes Drive Vortex Dynamics in Confined Bose-Einstein Condensates

N

Dynamics of a vortex in a trapped Bose-Einstein condensate

atoms (one atom is excited;

Correlated spontaneous emission on the Danube

N\ensuremath{-}1

Fluctuations in Ideal and Interacting Bose–Einstein Condensates: From the Laser Phase Transition Analogy to Squeezed States and Bogoliubov Quasiparticles ⁎

are in the ground state) and present an exact analytical expression for eigenvalues and eigenstates of this many-body problem. We found that some states decay much faster than the single-atom decay rate, while other states are trapped and undergo very slow decay. When the size of the atomic cloud is small compared with the radiation wavelength, we found that the radiation frequency undergoes a large shift.

Bohr model and dimensional scaling analysis of atoms and molecules

The dynamics of vortices in trapped Bose-Einstein condensates are investigated both analytically and numerically. In axially symmetric traps, the critical rotation frequency for metastability of an isolated vortex coincides with the largest vortex precession frequency (or anomalous mode) in the Bogoliubov excitation spectrum. The number of anomalous modes increases for an elongated condensate. The largest mode frequency exceeds the thermodynamic critical frequency and the nucleation frequency at which vortices are created dynamically. Thus, anomalous modes describe both vortex precession and the critical rotation frequency for creation of the first vortex in an elongated condensate.