We analyse dissipation in quantum computation and its destructive impact on efficiency of algorithms. Using a general model decoherence, we study the time evolution register arbitrary length coupled with an environment coherence length. discuss relations between decoherence computational complexity show that factorization algorithm must be modified order to regarded as efficient realistic.

In this paper we investigate the possibility to make complete Bell measurements on a product Hilbert space of two two-level bosonic systems. We restrict our tools linear elements, like beam splitters and phase shifters, delay lines electronically switched photo-detectors, auxiliary bosons. As result show that with these never failing measurement is impossible.

Open quantum systems that interact with structured reservoirs exhibit non-Markovian dynamics. We present a jump method for treating the dynamics of such systems. This approach is generalization standard Monte Carlo wave function (MCWF) Markovian The MCWF identifies decay rates probabilities and fails where time-dependent become temporarily negative. Our circumvents this problem provides an efficient unraveling ensemble

We present a review of wave-packet dynamics, with focus on 'femto-chemistry'. basic theory and simple properties wave-packets, the application two-state models to processes in presence light. also discuss treatment wave-packets dissipative problems.

We study the exact entanglement dynamics of two qubits in a common structured reservoir. demonstrate that for certain classes entangled states, sudden death occurs, while initially factorized birth takes place. The backaction non-Markovian reservoir is responsible revivals after has occurred, and also periods disentanglement following birth.

We discuss the properties of a simple and robust scheme for preparing atoms molecules in an arbitrary preselected coherent superposition quantum states - fractional stimulated Raman adiabatic passage (fractional STIRAP) first proposed by Marte et al (1991 Phys. Rev. A 44 R4118). As STIRAP, Stokes pulse arrives before pump pulse, but unlike here two pulses terminate simultaneously, while maintaining constant ratio amplitudes. extend earlier research suggest realization this with smoothly...

We present the process of adiabatic passage by light-induced potentials for transferring a wave packet from one molecular potential to displaced ground vibrational state another. The uses counterintuitive sequence light pulses couple three states. It shares many features with stimulated Raman passage, such as high efficiency and insensitivity pulse parameters. However, in former there is no two-photon resonance, main mechanism transport potential.

We discuss the advantages of using approximate quantum Fourier transform (AQFT) in algorithms which involve periodicity estimations. analyze networks performing AQFT presence decoherence and show that extensive approximations can be made before accuracy (as compared with regular transform) is compromised. for some computations an approximation may imply a better performance. \textcopyright{} 1996 The American Physical Society.

We discuss in detail how non-Markovian open system dynamics can be described terms of quantum jumps [J. Piilo et al., Phys. Rev. Lett. 100, 180402 (2008)]. Our results demonstrate that it is possible to have a jump description contained the physical Hilbert space reduced system. The developed approach generalization Markovian Monte Carlo wave function (MCWF) method into regime. conserves both probabilities density matrix and norms state vectors exactly sheds new light on dynamics. pure...

We investigate the non-Markovian dynamics of two-state systems in structured reservoirs. establish a connection between two theoretical quantum approaches, pseudomodes [B. M. Garraway, Phys. Rev. A 55, 2290 (1997)] and recently developed jump method [J. Piilo et al., Lett. 100, 180402 (2008)]. This provides clear physical picture how reservoir affects system dynamics, indicating role as an effective description environmental memory.

We present a scheme of the high-precise three-dimensional (3D) localization by measurement atomic-level population. The is applied to four-level tripod-type atom coupled three strong standing waves and probe running wave. As result, can be localized in volumes that are substantially smaller than cubic optical wavelength. upper-level distribution depends crucially on atom-field coupling it forms 3D periodic structures composed spheres, hourglasses, bowls, donuts, or deformed barrels.

In this Letter, we investigate the occurrence of Zeno and anti-Zeno effects for quantum Brownian motion. We single out parameters both system reservoir governing crossover between dynamics. demonstrate that, high temperatures, short time behavior environment induced decoherence is ultimately responsible either or effect. Finally, suggest a way to manipulate decay rate observe controlled continuous passage from suppression acceleration using engineered reservoirs in trapped ion context.

We set up a level-crossing model with two time scales and compare the numerically calculated probability transfer several analytic results. also examine in adiabatic limit make comparison calculation based on approach of Dykhne [Sov. Phys.---JETP 11, 411 (1960); 14, 941 (1962)] Davis Pechukas [J. Chem. Phys. 64, 3129 (1976)]. find that we can get an improved agreement if modify their approach.

Recent Feshbach-resonance experiments with 85Rb Bose-Einstein condensates have led to a host of unexplained results: dramatic losses condensate atoms for an across-resonance sweep the magnetic field, collapsing burst emanating from remnant condensate, increased decreasing interaction times, and coherent oscillations between atoms. Using simple yet realistic mean-field model, we find that rogue dissociation, molecular dissociation noncondensate atom pairs, is strongly implicated as physical...

In this paper we discuss the excitation of a localized molecular ground-state wave function by short laser pulse. With one-dimensional approach show when it is possible to excite considerable fraction ground state without too much distortion shape packet. This interest in time-resolved experiments where an excited packet often taken as initial state. We solve two coupled equations numerically and compare results analytical approximation based on Rosen-Zener model. The validity its breakdown...

We provide an analytical description of the entanglement dynamics two qubits coupled to a common structured reservoir at zero temperature. derive conditions maximize reservoir-induced for initially factorized state two-qubit system. In particular, when are placed inside lossy cavity, we show that high values can be obtained, even in bad-cavity limit, dispersive regime. Finally that, under certain conditions, exhibits quantum beats and explain their physical origin terms interference between...

We examine the effect of nonlinearity at a level crossing on probability for nonadiabatic transitions P. By using Dykhne-Davis-Pechukas formula, we derive simple analytic estimates P two types nonlinear crossings. In first type, in detuning appears as perturbative correction to dominant linear time dependence. Then appreciable deviations from Landau-Zener ${P}_{\mathrm{LZ}}$ are found appear large couplings only, when is small; this explains why model often seen provide more accurate results...

We calculate the light-induced collisional loss of laser-cooled and trapped magnesium atoms for detunings up to 50 atomic linewidths red ${}^{1}{S}_{0}{\ensuremath{-}}^{1}{P}_{1}$ cooling transition. evaluate rate coefficients due both radiative nonradiative state-changing mechanisms temperatures at below Doppler-cooling temperature. solve Schr\"odinger equation with a complex potential represent spontaneous decay, but also give analytic models various limits. Vibrational structure molecular...

I describe the current theories for cold collisions between laser-cooled and trapped neutral atoms in light fields. The emphasis is on dynamical nature of problem, i.e. collisional loss from trap or heating atomic cloud. recent work optical shielding also reviewed.

We have determined the rate of loss atoms from a Bose-Einstein condensed gas due to binary processes in presence far-detuned laser field. In this limit, spectrum is markedly different from, and can greatly exceed, basic atomic rate. suggest that measurements be used determine nature atom interactions condensate.

We demonstrate suppression of two-color photoassociative ionization in a sodium vapor magneto-optical trap by imposing an auxiliary "suppressor" light beam on the ensemble colliding trapped atoms. interpret experimental results terms simple picture which suppressor intercepts incoming reactant particle flux and reroutes it to long-range repulsive states, effectively preventing further approach collision pairs.

We present a simple but efficient geometrical method for determining the inert states of spin-$S$ systems. It can be used if system is described by spin vector particle and its energy invariant in rotations phase changes. Our applicable to an arbitrary $S$ it based on representation pure state terms $2S$ points surface sphere. use this find candidates some ground spinor Bose-Einstein condensates.

The dissipative dynamics of a quantum Brownian particle is studied for different types environment. We derive analytic results the time evolution mean energy system Ohmic, sub-Ohmic, and super-Ohmic environments, without performing Markovian approximation. Our allow one to establish direct link between form environmental spectrum thermalization dynamics. This in turn leads natural explanation microscopic physical processes ruling both short-time non-Markovian region long-time one....

We show by numerically solving the Bogoliubov--de Gennes equations and integrating Gross-Pitaevskii equation that onset of snake instability ring dark solitons requires a broken symmetry. elucidate explicitly connection between imaginary Bogoliubov modes instability, predicting number vortex-antivortex pairs produced. In addition, we propose simple model to give physical motivation as why takes place needs Finally, tight confinement in toroidal potential actually enhances soliton decay due...