arXiv subjects

Miroljub Dugic

Publications and source records attributed to Miroljub Dugic.

12 recordsLinked to original sources

arXiv2017

Kraus operators for a pair of interacting qubits: a case study

The Kraus form of the completely positive dynamical maps is appealing from the mathematical and the point of the diverse applications of the open quantum systems theory. Unfortunately, the Kraus operators are poorly known for the two-qubit processes. In this paper, we derive the Kraus operators for a pair of interacting qubit, while the strength of the interaction is arbitrary. One of the qubits is subjected to the x-projection spin measurement. The obtained results are applied to calculate the dynamics of the initial entanglement in the qubits system. We obtain the loss of the correlations in the finite time interval; the stronger the inter-qubit interaction, the longer lasting entanglement in the system.

quant-ph↗

arXiv2017

Generalized Kraus operators for the one-qubit depolarizing quantum channel

Microscopic Hamiltonian models of the composite system "open system + environment" typically do not provide the operator-sum Kraus form of the open system's dynamical map. With the use of a recently de- veloped method [16], we derive the Kraus operators starting from the mi- croscopic Hamiltonian model, i.e. from the proper master equation, of the one-qubit depolarizing channel. Those Kraus operators generalize the stan- dard counterparts, which are widely used in the literature. Comparison of the standard and the here obtained Kraus operators is performed via inves- tigating dynamical change of the Bloch sphere volume, entropy production and the open system's state trace distance. We find that the standard depo- larizing channel is more deteriorating than the generalized one.

quant-ph↗

arXiv2016

Collective versus individual classicality for a pair of interacting qubits immersed in independent local environments

There is current interest in investigating which variables play an important role in the physical processes with an open composite quan- tum system that ranges from the foundational issues to the tasks of diverse applications in quantum physics and technology. In this paper we contrast the local versus the collective classical-like behavior of a pair of interacting qubits immersed in the mutually independent thermal baths. The qubits can be locally subjected to any of the standard, microscopically modelled, generalized amplitude damping and phase damping channel, as well as to the recently introduced generalized depolarizing channel. As a criterion for the classical-like behavior we use the least entropy production, i.e. the total correlation in the system. The classical-like collective behavior is found for short time intervals for strongly interacting qubits. Only in a certain trivial case we observe the simultaneous collective and individual-qubits classical- ity. Observation (non-observation) of the collective (individual) classicality can reveal the kind and strength of the qubits interaction or the ratio of the qubits' energy-gaps, while manipulating the qubits interaction (by tuning the strength and/or refocussing) can give rise to the desired kind of classicality.

quant-ph↗

arXiv2014

Quantum Structures: A View of the Quantum World

We offer a systematic account of decomposition of quantum systems into parts. Different decompositions (structures) are mutually linked via the proper linear canonical transformations. Different kinds of structures, as well as their relations, are considered. Emphasis is placed on mutually global and irreducible structures. Is there a privileged structure of the closed system? Is there a preferred (bipartite) structure of an open system? Are there any practical advantages of certain alternative structures of the system? Is there a simple dynamical relation for a pair of structures? The [necessarily partial] answers are rather intriguing. Relativity of quantum correlations (that include entanglement as well as the "one-way" and "two-way" discord) is carefully presented. Emphasis is placed on the "parallel occurrence of decoherence" in the quantum Brownian motion. The environment-selected preferred structure of an open composite system is presented for a pair of harmonic oscillators (or the field modes). A limitation of the Nakajima-Zwanzig projection method appears as a consequence of quantum correlations relativity. Hence, describing dynamics of an alternate open-system is a delicate task. Certain interpretational issues, which include "quantum reference frames" issue, are discussed. Some recent experiments are also discussed. To this end, the option that "there are no particles" on the most fundamental physical level naturally follows. Certain open questions and prospects for further research are highlighted.

quant-ph↗

arXiv2005

Locality in Nonsequential Quantum Operations

We give an example of fulfillment of the condition of locality--no information transfer between certain subsystems--in a tripartite quantum system whose dynamics can not be decomposed (non-sequential dynamics of the system). The three subsystems ($A$, $B$ and $C$) are designed such that $C$ interacts simultaneously with both $A$ and $B$, while there is not any interaction between $A$ and $B$. On this basis, we emphasize validity of the condition of locality in a realistic physical situation.

quant-ph↗

arXiv2005

What is "system": some decoherence-theory arguments

We discuss the possibility of making the {\it initial} definitions of mutually different (possibly interacting, or even entangled) systems in the context of decoherence theory. We point out relativity of the concept of elementary physical system as well as point out complementarity of the different possible divisions of a composite system into "subsystems", thus eventually sharpening the issue of 'what is system'.

quant-ph↗

arXiv2002

On a Possible Physical Metatheory of Consciousness

We show that the modern quantum mechanics, and particularly the theory of decoherence, allows formulating a sort of a physical metatheory of consciousness. Particularly, the analysis of the necessary conditions for the occurrence of decoherence, along with the hypothesis that consciousness bears (more-or-less) well definable physical origin, leads to a wider physical picture naturally involving consciousness. This can be considered as a sort of a psycho-physical parallelism, but on very wide scales bearing some cosmological relevance.

quant-ph↗

arXiv2002

Quantum Parallelism in Quantum Information Processing

We investigate distinguishability (measured by fidelity) of the initial and the final state of a qubit, which is an object of the so-called nonideal quantum measurement of the first kind. We show that the fidelity of a nonideal measurement can be greater than the fidelity of the corresponding ideal measurement. This result is somewhat counterintuitive, and can be traced back to the quantum parallelism in quantum operations, in analogy with the quantum parallelism manifested in the quantum computing theory. In particular, while the quantum parallelism in quantum computing underlies efficient quantum algorithms, the quantum parallelism in quantum information theory underlies this, classically unexpected, increase of the fidelity.

quant-ph↗

arXiv2002

The zero energy quantum informtaiton processing

In contradistinction with some plausible statements of the information theory, we point out the possibility of the zero energy quantum information processing. Particularly, we investigate the rate of the entanglement formation in the operation of the quantum "oracles" employing the "quantum parallelism", and we obtain that the relative maximum of the rate of the operation distinguishes the zero average energy of interaction in the composite system "input register + output register". This result is reducible to neither of the previously obtained bounds, and therefore represents a new bound for the nonorthogonal state transformations in the quantum information theory.

quant-ph↗

arXiv2000

On a Physical Metatheory of Consciousness

We show that the modern quantum mechanics, and particularly the theory of decoherence, allows for formulating a sort of a physical metatheory of consciousness. Particularly, the analysis of the necessary conditions for the occurrence of decoherence, along with the hypothesis that consciousness bears (more-or-less) well definable physical origin, leads to a wider physical picture naturally involving consciousness. This can be considered as a sort of a psycho-physical parallelism, but on rather wide scales bearing some cosmological relevance.

quant-ph↗

arXiv1999

Quantum mechanical modeling of the CNOT (XOR) gate

We consider the CNOT quantum gate as a physical action, i.e. as unitary in time evolution of the two-qubit system. This points to the modeling of the interaction Hamiltonian of the two-qubit system which would correspond to the CNOT transformation; the analysis naturally generalizes to the Toffoli gate. Despite nonuniqueness of the model of the interaction Hamiltonian, the analysis distinguishes that the interaction Hamiltonian does not posses any global (rotational) symmetry. This forces us to conclude that the direct (non-mediated) interaction in the two-qubit system does not suffice for implementing the CNOT gate. I.e., so as to be able succesfully to implement the CNOT transformation, a mediator (i.e. an external physical system interacting with both of the qubits) is required.

quant-ph↗

arXiv1998

Many Time Interpretation Of the Quantum Measurement Process

Many Time Interpretation (MTI) proposes that each stochastic "quantum jump" ("reduction") concerning each single object (of an ensemble) represents a consequence of a (stochastic) choice (change) of Time. Therefore, each single object experiences its own (local), stochastically chosen Time, which is as real for it, as the macroscopic Time is real in classical physics. Therefore, instead of the "indeterminism" with regard to the macroscopic Time, MTI proposes "determinism", but with regard to the set(s) of (stochastically chosen) local Times. Within an axiomatization, which includes the composite system "single object+apparatus+environment, MTI leads to : (i) Recognizing the amplification process as the fundamental "part" of the measurement process, (ii) Nonvalidity of the Schrodinger equation concerning the "whole", O+A+E, which makes the "state reduction process" unnecessary and unphysical, (iii) Natural deducibility of the macroscopic irreversibility, and (iv) Nonequivalence of MTI with any existing measurement theory, or interpretation. Thus, within MTI, the measurement problem reduces basically onto the search for quantum effect, which would allow forthe local, stochastic change of Time.

quant-ph↗