Counting statistics of collective photon transmissions

We theoretically study cooperative effects in the steady-state transmission of photons through a medium of N radiators. Using methods from quantum transport, we find a cross-over in scaling from N to N² in the current and to even higher powers of N in the higher cumulants of the photon counting statistics as a function of the tunable source occupation. The effect should be observable for atoms confined within a nano-cell with a pumped optical cavity as photon source.     

Counting statistics of non-Markovian quantum stochastic processes

We derive a general expression for the cumulant generating function (CGF) of non-Markovian quantum stochastic transport processes. The long-time limit of the CGF is determined by a single dominating pole of the resolvent of the memory kernel from which we extract the zero-frequency cumulants of the current using a recursive scheme. The finite-frequency noise is expressed not only in terms of the resolvent, but also initial system-environment correlations. As an illustrative example we consider electron transport through a dissipative double quantum dot for which we study the effects of dissipation on the zero-frequency cumulants of high orders and the finite-frequency noise.     

Counting statistics and detector properties of quantum point contacts

Quantum detector properties of the quantum point contact (QPC) are analyzed for an arbitrary electron transparency and coupling strength to the measured system and are shown to be determined by the electron counting statistics. Conditions of the quantum-limited operation of the QPC detector, which prevent information loss through the scattering time and scattering phases, are found for arbitrary coupling. We show that the phase information can be restored and used for the quantum-limited detection by inclusion of the QPC detector in the electronic Mach-Zehnder interferometer.     

Counting statistics of photons produced by electronic shot noise

A theory is presented for the photodetection statistics of radiation produced by current fluctuations in a phase-coherent conductor. Deviations are found from the Poisson statistics that would result from a classical current. For detection in a narrow frequency interval delta omega, the photocount distribution has the negative-binomial form of blackbody radiation if e delta omega is less than the mean current I in the conductor. When electronic localization sets in, I drops below e delta omega and a different type of super-Poissonian photon statistics results.     

Counting statistics of single electron transport in a quantum dot

We have measured the full counting statistics of current fluctuations in a semiconductor quantum dot (QD) by real-time detection of single electron tunneling with a quantum point contact. This method gives direct access to the distribution function of current fluctuations. Suppression of the second moment (related to the shot noise) and the third moment (related to the asymmetry of the distribution) in a tunable semiconductor QD is demonstrated experimentally. With this method we demonstrate the ability to measure very low current and noise levels.     

The spatial form of an adiabatic jet

By considering the boundary of a jet as a discontinuity, the ratio of the boundary shock velocity and the axial flow velocity may be regarded as the spatial derivative of the boundary curve. The obtained equation can be solved asymptotically.     

On an adiabatic theory of multielectron systems

An adiabatic approximation is constructed for the outer atomic electron using its weak bond as compared to other electrons. The adiabatic approach is well-grounded for a helium atom and is extended to other atoms and crystals of rare gases, a functional dependence being established between electron properties of crystals and free atom constants.     

Counting defects in an instantaneous quench

We consider the formation of defects in a nonequilibrium second-order phase transition induced by an instantaneous quench to zero temperature in a type II superconductor. We perform a full nonlinear simulation where we follow the evolution in time of the local order parameter field. We determine how far into the phase transition theoretical estimates of the defect density based on the Gaussian approximation yield a reliable prediction for the actual density. We also characterize quantitatively some aspects of the out of equilibrium phase transition.     

Accelerating an adiabatic process by nonlinear sweeping

We investigate the acceleration of an adiabatic process with the same survival probability of the ground state by sweeping a parameter nonlinearly, fast in the wide gap region and slowly in the narrow gap region, in contrast to the usual linear sweeping. We find the expected acceleration both in the Landau-Zener tunneling model and in the adiabatic quantum computing model for factorizing the number N - 21.     

Experimental implementation of an adiabatic quantum optimization algorithm

We report the realization of a nuclear magnetic resonance computer with three quantum bits that simulates an adiabatic quantum optimization algorithm. Adiabatic quantum algorithms offer new insight into how quantum resources can be used to solve hard problems. This experiment uses a particularly well-suited three quantum bit molecule and was made possible by introducing a technique that encodes general instances of the given optimization problem into an easily applicable Hamiltonian. Our results indicate an optimal run time of the adiabatic algorithm that agrees well with the prediction of a simple decoherence model.     

On an adiabatic invariant in the thermodynamics of solids

A thermodynamic invariant in the form of the ratio of a vibrational frequency in an anharmonic solid to the temperature in adiabatic processes is derived. The adiabatic invariance established is used to derive in a simple manner an expression for the temperature change due to elastic adiabatic loading of solids (Kelvin's equation). Fiz. Tverd. Tela (St. Petersburg) 41, 134–136 (January 1999)     

CNOT gate by adiabatic passage with an optical cavity

We propose a scheme for the construction of a CNOT gate by adiabatic passage in an optical cavity. In opposition to a previously proposed method, the technique is not based on fractional adiabatic passage, which requires the control of the ratio of two pulse amplitudes. Moreover, the technique constitutes a decoherence-free method in the sense that spontaneous emission and cavity damping are avoided since the dynamics follows dark states.     

Reconstruction of attosecond pulse trains using an adiabatic phase expansion

We propose a new method to reconstruct the electric field of attosecond pulse trains. The phase of the high-order harmonic emission electric field is Taylor expanded around the maximum of the laser pulse envelope in the time domain and around the central harmonic in the frequency domain. Experimental measurements allow us to determine the coefficients of this expansion and to characterize the radiation with attosecond accuracy over a femtosecond time scale. The method gives access to pulse-to-pulse variations along the train, including the timing, the chirp, and the attosecond carrier envelope phase.     

Counting atoms using interaction blockade in an optical superlattice

We report on the observation of an interaction blockade effect for ultracold atoms in optical lattices, analogous to the Coulomb blockade observed in mesoscopic solid state systems. When the lattice sites are converted into biased double wells, we detect a discrete set of steps in the well population for increasing bias potentials. These correspond to tunneling resonances where the atom number on each side of the barrier changes one by one. This allows us to count and control the number of atoms within a given well. By evaluating the amplitude of the different plateaus, we can fully determine the number distribution of the atoms in the lattice, which we demonstrate for the case of a superfluid and Mott insulating regime of 87Rb.     

Modeling an adiabatic quantum computer via an exact map to a gas of particles

We map adiabatic quantum evolution on the classical Hamiltonian dynamics of a 1D gas (Pechukas gas) and simulate the latter numerically. This approach turns out to be both insightful and numerically efficient, as seen from our example of a CNOT gate simulation. For a general class of Hamiltonians we show that the escape probability from the initial state scales no faster than |lambda|gamma, where |lambda| is the adiabaticity parameter. The scaling exponent for the escape probability is gamma=1/2 for all levels, except the edge (bottom and top) ones, where gamma approximately < 1/3. In principle, our method can solve arbitrarily large adiabatic quantum Hamiltonians.     

Derivation of an adiabatic time-dependent Hartree-Fock formalism from a variational principle

A derivation of the adiabatic time-dependent Hartree-Fock formalism is given, which is based on a variational principle analogous to Hamilton's principle in classical mechanics. The method leads to a Hamiltonian for collective motion which separates into a potential and a kinetic energy and gives mass and potential parameters in terms of the nucleon-nucleon interaction. The adiabatic approximation assumes slow motion but not small amplitudes and can therefore describe anharmonic effects. The RPA is a limiting case where both amplitudes and velocities are small. The variational approach provides a consistent way of extracting coordinates and momenta from the density matrix and of obtaining equations of motion when particular trial forms for this density matrix are chosen. One such choice leads to Thouless-Valatin formula. An other choice leads to irrotational hydrodynamics.     

Inflaton field potential producing an exactly flat spectrum of adiabatic perturbations

Presented in this letter is the exact solution of the problem of finding the potential of an inflaton scalar field for which adiabatic perturbations generated during a de Sitter (inflationary) stage in the early Universe have an exactly flat (or, the Harrison-Zeldovich) initial spectrum. This solution lies outside the scope of the slow-roll approximation and higher-order corrections to it. The potential found depends on two arbitrary physical constants, one of which determines the amplitude of the perturbations. For small (zero) values of the other constant, a long (infinite) inflationary stage with slow rolling of the inflaton field exists.     

Inversion temperature for adiabatic evaporation of liquid into an air-steam mixture

This paper deals with adiabatic evaporation of various liquids into an air-steam mixture and pure superheated steam. The focus is made on the inversion temperature, which means that the rate of liquid evaporation into an air-steam mixture (superheated steam) becomes equal to the rate of evaporation into dry air. A simple analytical solution for finding of inversion temperature was derived, and the required conditions of existence of the given phenomenon are found. The influence of parameters of the main flow (vapor quantity, pressure, and flow regime) on the value of inversion temperature is analysed. It is shown that consideration of the influence of injection flow on relative function of heat transfer for inversion temperature definition of ethanol, acetone, and benzene is necessary. A comparison with numerical modelling was made to estimate the analytical solution accuracy. The work was financially supported by the Russian Foundation for Basic Research (Grants Nos. 05-02-16478 and 05-08-17981), and by President of the Russian Federation (Grant NSh-6965.2006.8).