Virtual quantum subsystems

The physical resources available to access and manipulate the degrees of freedom of a quantum system define the set A of operationally relevant observables. The algebraic structure of A selects a preferred tensor product structure, i.e., a partition into subsystems. The notion of compoundness for quantum systems is accordingly relativized. Universal control over virtual subsystems can be achieved by using quantum noncommutative holonomies     

Energy dependence on fractional charge for strongly interacting subsystems

The energies of a pair of strongly interacting subsystems with arbitrary noninteger charges are examined from closed- and open-system perspectives. An ensemble representation of the charge dependence is derived, valid at all interaction strengths. Transforming from resonance-state ionicity to ensemble charge dependence imposes physical constraints on the occupation numbers in the strong-interaction limit. For open systems, the chemical potential is evaluated using microscopic and thermodynamic models, leading to a novel correlation between ground-state charge and an electronic temperature.     

Separated subsystems in four-level atom

We study a four-level system with two lasers. We show that under certain conditions it is possible to group our four-level system into two completely separated two-level subsystems and this separation holds when the detunings and the Rabi frequencies in our system are time-dependent.     

Fluctuation interaction of Ising subsystems

A phase diagram of two Ising subsystems σ and s has been constructed on a Bethe lattice with a coordination number 4 (a simplified analog of a square lattice). In contrast to the known Ashkin-Teller model, the interaction between these two subsystems is of a purely fluctuational nature; i.e., it does not manifest itself in the ground state and nullifies the sums of the products of average spins 〈σ〉〈s〉 (interactions of this type are realized in lattice-type adsorbed systems with dipolelike intermolecular interactions and strong azimuthal angular dependence of the adsorption potential of symmetry C₄). Apart from conventional states, i.e., a high-temperature disordered state (〈σ〉=〈s〉=0) and a low-temperature ordered state (〈σ〉 and 〈s〉 =? 0), this system can also exist in a correlated state (〈σs〉 =? 0 at 〈σ〉=〈s〉=0). In the theory of orientational phase transitions, this state corresponds to a fundamentally different, intermediate (on the temperature axis) phase in which a preferred direction of long molecule axes arises in the absence of spontaneous polarization. The results of Monte Carlo simulation on a square lattice agree with the conclusions obtained on a Bethe lattice. The characteristics of the orientational phase transition in a 2 × 1 monolayer of CO molecules adsorbed on the NaCl(100) surface are discussed.     

Probability relations involving several subsystems

We consider the question of factorizability in tensor product spaces, and argue that the correlations associated with entangled states are even more problematic in the general case involving any tensor product of Hilbert spaces, than in the Einstein, Podolsky, and Rosen case with only two [1].     

Topological protection and quantum noiseless subsystems

Encoding and manipulation of quantum information by means of topological degrees of freedom provides a promising way to achieve natural fault tolerance that is built in at the physical level. We show that this topological approach to quantum information processing is a particular instance of the notion of computation in a noiseless quantum subsystem. The latter then provides the most general conceptual framework for stabilizing quantum information and for preserving quantum coherence in topological and geometric systems.     

Dynamical generation of noiseless quantum subsystems

We combine dynamical decoupling and universal control methods for open quantum systems with coding procedures. By exploiting a general algebraic approach, we show how appropriate encodings of quantum states result in obtaining universal control over dynamically generated noise-protected subsystems with limited control resources. In particular, we provide a constructive scheme based on two-body Hamiltonians for performing universal quantum computation over large noiseless spaces which can be engineered in the presence of arbitrary linear quantum noise.     

Method to find quantum noiseless subsystems

We develop a structure theory for decoherence-free subspaces and noiseless subsystems that applies to arbitrary (not necessarily unital) quantum operations. The theory can be alternatively phrased in terms of the superoperator perspective, or the algebraic noise commutant formalism. As an application, we propose a method for finding all such subspaces and subsystems for arbitrary quantum operations. We suggest that this work brings the fundamental passive technique for error correction in quantum computing an important step closer to practical realization.     

激光装置片状放大器组件的氙灯可靠性分析

 整理惯性约束聚变激光装置的运行记录和氙灯的故障数据,得到10种氙灯故障现象,并且归纳为3类,即触发故障、绝缘故障和氙灯爆炸,按故障发生时间可以分为“引发失效”的故障和“舍生取义”的故障。分析3类氙灯故障与片状放大器组件以及装置打靶成功率的逻辑关系,生成基于氙灯故障的装置打靶故障树,描述氙灯可靠性对于装置打靶成功的重要性。分析氙灯的生产工艺流程和工艺缺陷,生成氙灯的故障与工艺的鱼刺图,揭示氙灯故障的根源。     

激光装置片状放大器组件的氙灯可靠性分析

整理惯性约束聚变激光装置的运行记录和氙灯的故障数据,得到10种氙灯故障现象,并且归纳为3类,即触发故障、绝缘故障和氙灯爆炸,按故障发生时间可以分为“引发失效”的故障和“舍生取义”的故障。分析3类氙灯故障与片状放大器组件以及装置打靶成功率的逻辑关系,生成基于氙灯故障的装置打靶故障树,描述氙灯可靠性对于装置打靶成功的重要性。分析氙灯的生产工艺流程和工艺缺陷,生成氙灯的故障与工艺的鱼刺图,揭示氙灯故障的根源。     

Quasi-additivity of Tsallis entropies and correlated subsystems

We use Beck's quasi-additivity of Tsallis entropies for n   independent subsystems to show that like the case of n=2$n=2$, the entropic index q$q$ approaches 1 by increasing system size. Then, we will generalize that concept to correlated subsystems to find that in the case of correlated subsystems, when system size increases, q$q$ also approaches a value corresponding to the additive case.     

Ordering of interacting subsystems. Molecular dynamics

The molecular dynamics method is used to examine the ordering of interacting subsystems in a two-component, two-dimensional Coulomb gas, consisting of equal amounts of positively and negatively charged particles, which simulates the behavior of a system of interacting vortices. In particular, it is found that when the system temperature is lowered from the Kosterlitz-Thouless transition point, additional ordering of the vortex chains may take place. It is noted that this process may stimulate the development of vortex chains observed in real superfluid, magnetic, and superconducting systems. Possible applications of the molecular dynamics method to phase separation and the ordering of adiabatically slowly moving subsystems in the collective field of a fast subsystem are considered. Fiz. Tverd. Tela (St. Petersburg) 40, 1701–1704 (September 1998)     

Phase transitions in crystals with competitive Jahn-Teller subsystems

A statistical thermodynamic model of phase transformations caused by the cooperative Jahn-Teller effect in spinels containing two types of Jahn-Teller cations has been proposed. It has been shown that the specific features of the phase diagrams of compounds similar to Cu_{1 ? x} Ni _x Cr₂O₄, such as the presence of one orthorhombic and two anti-isostructural tetragonal phases, are associated with the competition between orderings of the subsystems of tetrahedra distorted due to the Jahn-Teller effect. The degree and character of the ordering of each subsystem of the solid solution have been determined. The main factors responsible for the thermodynamic properties and phase diagrams, in particular, the conditions for splitting of an isolated critical point into two triple points, have been investigated.     

Entangled states in spin subsystems of polyatomic ensembles

The feasibility of formation entangled states in spin subsystems of two spatially separated atomic ensembles is discussed. It is shown that the process of cooperative Raman scattering of correlated photon pairs emitted by a parametric source in a below-threshold regime may serve as a physical mechanism for the entanglement. A scheme of teleportation of a coherent spin state in systems of spatially separated ensembles is proposed.     

On entanglement of quantum states of noninteracting subsystems

Simple models for measuring the characteristics of a system of two atoms that do not interact with each other are used to show that the nonselectivity of measurement, related to the indistinguishability of the quantum subsystems with respect to some general parameter, leads to entanglement of the atomic states of the subsystem selected in such a way. This entanglement is in no way related to some collective process and is only due to the effective measurement in an entangled basis. An analogy between the preparation of entangled states of a system of subsystems that do not interact with each other by a quantum reduction (a measurement) and a quantum evolution is found.     

Spectral representations and the density matrix of subsystems

A regular method is indicated which makes it possible, under conditions of thermodynamic equilibrium, to find in a constructive manner the density matrix of a subsystem which, in general, is in strong interaction with its surroundings.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 81–87, May, 1978.I am grateful to the participants of the seminar led by V. L. Bonch-Bruevich for discussion of the work.     

Random response of identical,one-dimensional coupled subsystems

A precise statistical analysis is carried out for the steady-state response of a one-dimensional wave-bearing system formed from two identical subsystems coupled together at an end with a general coupling. The statistics correspond approximately to averaging in frequency. Cross-correlation between the wave fields incident on the coupling in the two subsystems (neglected in most statistical analyses) strongly affects the magnitude of the coupling power and, for dissipative couplings, the dissipative power. Asymmetry of the wave field in each subsystem (also usually neglected) can have a significant additional effect even when the dissipative loss factor is small. These effects are evaluated, and their analogs in analyses based in modal theory are discussed.     

Interaction of two spin subsystems with different wavevectors

The possibility of the transition of a spin system from an incommensurable to a commensurable phase via a phase with different wavevectors of individual subsystems is shown in the mean-field approximation.