arXiv subjects

Dmitry Solenov

Publications and source records attributed to Dmitry Solenov.

32 records · Page 2Linked to original sources

arXiv2008

On stability of odd-frequency superconducting state

Odd-frequency pairing mechanism of superconductivity has been investigated for several decades. Nevertheless, its properties, including the thermodynamic stability, have remained unclear. In particular, it has been argued that the odd-frequency state is thermodynamically unstable, has an unphysical (anti-) Meissner effect, and thus can not exist as a homogeneous equilibrium phase. We argue that this conclusion is incorrect because it implicitly relies on the inappropriate assumption that the odd-frequency superconductor can be described by an effective Hamiltonian that breaks the particle conservation symmetry. We demonstrate that the odd-frequency state can be properly described within the functional integral approach using non-local-in-time effective action. Within the saddle point approximation, we find that this phase is thermodynamically stable, exhibits ordinary Meissner effect, and therefore can be realized as an equilibrium homogenous state of matter.

cond-mat.supr-con↗

arXiv2008

Quantum Nucleation and Macroscopic Quantum Tunneling in Cold-Atom Boson-Fermion Mixtures

Kinetics of phase separation transition in boson-fermion cold atom mixtures is investigated. We identify the parameters at which the transition is governed by quantum nucleation mechanism, responsible for the formation of critical nuclei of a stable phase. We demonstrate that for low fermion-boson mass ratio the density dependence of quantum nucleation transition rate is experimentally observable. The crossover to macroscopic quantum tunneling regime is analyzed. Based on a microscopic description of interacting cold atom boson-fermion mixtures we derive an effective action for the critical droplet and obtain an asymptotic expression for the nucleation rate in the vicinity of the phase transition and near the spinodal instability of the mixed phase. We show that dissipation due to excitations in fermion subsystem play a dominant role close to the transition point.

cond-mat.mes-hall↗

arXiv2008

Kinetics of the Phase Separation Transition in Cold-Atom Boson-Fermion Mixtures

We study the kinetics of the first order phase separation transition in boson-fermion cold-atom mixtures. At sufficiently low temperatures such a transition is driven by quantum fluctuations responsible for the formation of critical nuclei of a stable phase. Based on a microscopic description of interacting boson-fermion mixtures we derive an effective action for the critical droplet and obtain an asymptotic expression for the nucleation rate in the vicinity of the phase transition and near the spinodal instability of the mixed phase. We also discuss effects of dissipation which play a dominant role close to the transition point, and identify the regimes where quantum nucleation can be experimentally observed in cold-atom systems.

cond-mat.mes-hall↗

arXiv2007

Unbalanced Renormalization of Tunneling in MOSFET-type Structures in Strong High-Frequency Electric Fields

Two-dimensional electron gas coupled to adjacent impurity sites in high-frequency out-of-plane ac control electric field is investigated. Modification of tunneling rates as a function of the field amplitude is calculated. Nonlinear dependence on the ac field strength is reported for the conductivity of two-dimensional electron gas. It develops a periodic peak structure.

cond-mat.mes-hall↗

arXiv2007

Entanglement and Quantum Noise Due to a Thermal Bosonic Field

We analyze the indirect exchange interaction between two two-state systems, e.g., spins 1/2, subject to a common finite-temperature environment modeled by bosonic modes. The environmental modes, e.g., phonons or cavity photons, are also a source of quantum noise. We analyze the coherent vs noise-induced features of the two-spin dynamics and predict that for low enough temperatures the induced interaction is coherent over time scales sufficient to create entanglement. A nonperturbative approach is utilized to obtain an exact solution for the onset of the induced interaction, whereas for large times, a Markovian scheme is used. We identify the time scales for which the spins develop entanglement for various spatial separations. For large enough times, the initially created entanglement is erased by quantum noise. Estimates for the interaction and the level of quantum noise for localized impurity electron spins in Si-Ge type semiconductors are given.

cond-mat.mes-hall↗

arXiv2006

Quantum phase transition in the multi-mode Dicke model

An investigation of the quantum phase transition in both discrete and continuum field Dicke models is presented. A series of anticrossing features following the criticality is revealed in the band of the field modes. Critical exponents are calculated. We investigate the properties of a pairwise entanglement measured by a concurrence and obtain analytical results in the thermodynamic limit.

cond-mat.mes-hall↗

arXiv2006

Decoherence of Dynamically Manipulated Qubits

We summarize our results on decoherence for short- to intermediate-time dynamics of an externally controlled two-state quantum system - a qubit - interacting with thermal bosonic environment. The developed approximation schemes are illustrated for an adiabatic model with time-dependent gate control, and for a model with rotating-wave gate function.

quant-ph↗

arXiv2006

Onset of Entanglement and Noise Cross-Correlations in Two-Qubit System Interacting with Common Bosonic Bath

We summarize our recent results for the induced exchange interaction due to thermal bosonic environment (bath) which also generates quantum noise. Our focus here is on the onset of the interaction. We demonstrate that the induced interaction can be used to manipulate and create entanglement over time scales sufficiently large for controlling the two-qubit system for quantum computing applications, though ultimately the noise effects will dominate.

quant-ph↗

arXiv2006

Coherent Interaction of Spins Induced by Thermal Bosonic Environment

We obtain and analyze the indirect exchange interaction between two two-state systems, e.g., spins, in a formulation that also incorporates the quantum noise that they experience, due to a bosonic environment, for instance, phonons. We utilize a perturbative approach to obtain a quantum evolution equation for the two-spin dynamics. A non-perturbative approach is used to study the onset of the induced interaction, which is calculated exactly. We predict that for low enough temperatures the interaction is coherent over time scales sufficient to create entanglement, dominated by the zero-point quantum fluctuations of the environment. We identify the time scales for which the spins develop entanglement for various spatial separations.

cond-mat.mes-hall↗

arXiv2005

Evaluation of Decoherence for Quantum Computing Architectures: Qubit System Subject to Time-Dependent Control

We present an approach that allows quantifying decoherence processes in an open quantum system subject to external time-dependent control. Interactions with the environment are modeled by a standard bosonic heat bath. We develop two unitarity-preserving approximation schemes to calculate the reduced density matrix. One of the approximations relies on a short-time factorization of the evolution operator, while the other utilizes expansion in terms of the system-bath coupling strength. Applications are reported for two illustrative systems: an exactly solvable adiabatic model, and a model of a rotating-wave quantumcomputing gate function. The approximations are found to produce consistent results at short and intermediate times.

cond-mat.mes-hall↗

arXiv2005

Non-Unitary Quantum Walks on Hyper-Cycles

We present analytical treatment of quantum walks on multidimensional hyper-cycle graphs. We derive the analytical expression of the probability distribution for strong and weak decoherence regimes. Upper bound to mixing time is obtained.

quant-ph↗

arXiv2005

Mixing and Decoherence in Continuous-Time Quantum Walks on Cycles

We prove analytical results showing that decoherence can be useful for mixing time in a continuous-time quantum walk on finite cycles. This complements the numerical observations by Kendon and Tregenna (Physical Review A 67 (2003), 042315) of a similar phenomenon for discrete-time quantum walks. Our analytical treatment of continuous-time quantum walks includes a continuous monitoring of all vertices that induces the decoherence process. We identify the dynamics of the probability distribution and observe how mixing times undergo the transition from quantum to classical behavior as our decoherence parameter grows from zero to infinity. Our results show that, for small rates of decoherence, the mixing time improves linearly with decoherence, whereas for large rates of decoherence, the mixing time deteriorates linearly towards the classical limit. In the middle region of decoherence rates, our numerical data confirms the existence of a unique optimal rate for which the mixing time is minimized.

quant-ph↗

arXiv2005

Continuous-time Quantum Walks on a Cycle Graph

We present analytical treatment of quantum walks on a cycle graph. The investigation is based on a realistic physical model of the graph in which decoherence is induced by continuous monitoring of each graph vertex with nearby quantum point contact. We derive the analytical expression of the probability distribution along the cycle. Upper bound estimate to mixing time is shown.

quant-ph↗

arXiv2004

Models of Short-Time Qubit Decoherence

We compare approaches to evaluation of decoherence at low temperatures in two-state quantum systems weakly coupled to the environment. By analyzing an exactly solvable model, we demonstrate that a non-Markovian approximation scheme yields good quality estimates of the reduced density matrix for time scales appropriate for evaluation of quantum computing designs.

cond-mat.mes-hall↗