arXiv subjects

Yuri I. Ozhigov

Publications and source records attributed to Yuri I. Ozhigov.

13 recordsLinked to original sources

arXiv2022

Three principles of quantum computing

The point of building a quantum computer is that it allows to model living things with predictive power and gives the opportunity to control life. Its scaling means not just the improvement of the instrument part, but also, mainly, mathematical and software tools, and our understanding of the QC problem. The first principle of quantum modeling is the reduction of reality to finite-dimensional models similar to QED in optical cavities. The second principle is a strict limitation of the so-called Feynman principle, the number of qubits in the standard formulation of the QC. This means treating decoherence exclusively as a limitation of the memory of a classical modeling computer, and introducing corresponding progressive restrictions on the working area of the Hilbert space of quantum states as the model expands. The third principle is similarity in processes of different nature. The quantum nature of reality is manifested in this principle; its nature is quantum nonlocality, which is the main property that ensures the prospects of quantum physical devices and their radical advantage over classical ones.

quant-ph↗

arXiv2021

The complexity of a quantum system and the accuracy of its description

The complexity of the quantum state of a multiparticle system and the maximum possible accuracy of its quantum description are connected by a relation similar to the coordinate-momentum uncertainty relation. The coefficient in this relation is equal to the maximum number of qubits whose dynamics can be adequately described by quantum theory, and therefore it can be determined experimentally through Grover search algorithm. Such a restriction of the Copenhagen formalism is relevant for complex systems; it gives a natural description of unitary dynamics together with decoherence and measurement, but also implies the existence of a minimum non-zero amplitude size, as well as a restriction on the equality of bases in the state space. The quantization of the amplitude allows us to formally introduce a certain kind of determinism into quantum evolution, which is important for complex systems.

quant-ph↗

arXiv2021

Quantum computations (course of lectures)

This course of lectures has been taught for several years at the Lomonosov Moscow State University; its modified version in 2021 is read in the Zhejiang University (Hangzhou), in the framework of summer school on quantum computing. The course is devoted to a new type of computations based on quantum mechanics. Quantum computations are fundamentally different from classical ones in that they occur in the space of so-called quantum states, and not in ordinary binary strings. Quantum computing is a real process in which the mathematical description is inextricably linked with quantum physics. Various forms of quantum computing are considered: the Feynman gate model, fermionic and adiabatic computations. A class of problems is described in which quantum computing is not only more efficient than classical ones, but also cannot be replaced by them. The course is designed for students of physics and mathematics and natural science specialties as well as all those interested in this subject. It requires familiarity with the basics of linear algebra and mathematical analysis in the first two courses of the university.

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arXiv2019

Space of dark states in Tavis-Cummings model

The dark states of a group of two-level atoms in the Tavis-Cummings resonator with zero detuning are considered. In these states, atoms can not emit photons, although they have non-zero energy. They are stable and can serve as a controlled energy reservoir from which photons can be extracted by differentiated effects on atoms, for example, their spatial separation. Dark states are the simplest example of a subspace free of decoherence in the form of a photon flight, and therefore are of interest for quantum computing. It is proved that a) the dimension of the subspace of dark states of atoms is the Catalan numbers, b) in the RWA approximation, any dark state is a linear combination of tensor products of singlet-type states and the ground states of individual atoms. For the exact model, in the case of the same force of interaction of atoms with the field, the same decomposition is true, and only singlets participate in the products and the dark states can neither emit a photon nor absorb it. The proof is based on the method of quantization of the amplitude of states of atomic ensembles, in which the roles of individual atoms are interchangeable. In such an ensemble there is a possibility of micro-causality: the trajectory of each quantum of amplitude can be uniquely assigned.

quant-ph↗

arXiv2018

Collective micro-causality in homogeneous quantum ensembles

It is shown that for quantum ensembles consisting of equal particles, the collective micro-causality does not contradict the quantum theory. The amplitudes of the states of such an ensemble can be divided into small portions, for each of which evolution in time will be accurately determined, without any randomness. For ensembles of dissimilar particles, whose Hamiltonian is represented as a sum of operators belonging to homogeneous systems, micro-causality will take place on separate small segments, on which only the selected component will act. In this case, the duration of the terms for different ensembles will be different. Micro causality is a consequence of the quantization of amplitudes, which plays a peculiar role for complex systems in which the amplitudes of individual states are very small. For such systems, the stochastic description, typical in the standard quantum theory should be replaced by a causal, i.e. deterministic one. In the article micro-causality is illustrated by the example of ensembles of two-level atoms in an optical cavity, considered under the Tavis-Cummings model in the rotating wave approximation; however, the conclusions are general.

physics.gen-ph↗

arXiv2017

Quantum lock on dark states

We propose quantum protection circuit (quantum lock), based on dark states of ensembles of two-level atoms in optical cavity. The secret key is the splitting of atoms into pairs, and publicly accessible part of the lock is the tensor product of EPR singlets, corresponding to the given splitting. To open the lock one must move synchronously pairs of atoms from the correct splitting to the other cavity; the lock will open if atoms do not emit photons. This scheme has perfect secrecy: it is impossible to hack it, even with effective solutions of any classical computational problems, in contrast to the RSA scheme. The method of obtaining dark states through Stark shift of atomic excitation energy is also proposed. This scheme makes possible to create secret keys of a few tens of atoms that is sufficient for the most practical applications.

quant-ph↗

arXiv2015

Dark states of atomic ensembles

Ensemble of identical two level atoms in dark state neither adsorbs nor emits photons due to destructive interference. It can be used for the source of energy for nano-devices. In Tavis-Cummings cavity the change of light-atom coupling cannot destroy the dark state. We propose the method of dark states preparation based on photon pumping and drain from the optical cavity with two atoms, one from which has Stark or Zeeman splitting of energy levels. This splitting is removed before photon drain from the cavity. The dark state yield after one such cycle has the order of energy level splitting. We show the scheme of the experiment, in which such cycles repeat until the dark state is produced with high probability and the results of computer simulation.

quant-ph↗

arXiv2015

Conductivity measurements in JCH like models

We consider the conductivity of excitations in short chains of optical cavities with two-level atoms in the models of JCH type, where either we explicitly take into account the photon jumps between atoms, or is merely a transfer of excitation from atom to atom. We found a non-trivial dependence of the conductivity on the intensity of runoff and inflow (quantum bottleneck) in the presence of dephasing noise (the effect of dephasing assisted transport).

quant-ph↗

arXiv2015

How to check quantum mechanics independently (Reply to arXiv:1505.04293)

This is the reply to the paper of Andrei Khrennikov arXiv:1505.04293 in which he expresses dissatisfaction with that the rough data in quantum experiments is not easily available and compares it with the open rough data in genetics. I try to explain why quantum experiments rough data is closed and why it differs radically from the biological. I also tried to answer the more thorny issue: is it possible to check quantum mechanics independently of other humans, e.g. trusting nobody.

physics.gen-ph↗

arXiv2013

Quantum selfish gene (biological evolution in terms of quantum mechanics)

I propose to treat the biological evolution of genoms by means of quantum mechanical tools. We start with the concept of meta- gene, which specifies the "selfish gene" of R.Dawkins. Meta- gene encodes the abstract living unity, which can live relatively independently of the others, and can contain a few real creatures. Each population of living creatures we treat as the wave function on meta- genes, which module squared is the total number of creatures with the given meta-gene, and the phase is the sum of "aspirations" to change the classical states of meta- genes. Each individual life thus becomes one of possible outcomes of the virtual quantum measurement of this function. The evolution of genomes is described by the unitary operator in the space of psi-functions or by Kossovsky-Lindblad equation in the case of open biosystems. This operator contains all the information about specific conditions under which individuals are, and how "aspirations" of their meta- genes may be implemented at the biochemical level. We show the example of quantum description of the population with two parts of meta-gene: "wolves" and "deer", which can be simultaneously in the same abstract living unity. "Selfish gene" reconciled with the notion of individuality of alive beings that gives possibility to consider evolutionary scenarios and their possible physical causes from the single position.

physics.gen-ph↗

arXiv2012

Entanglement in systems of oscillators and quantum computations

It is shown that quantum devices based only on oscillators cannot serve as the universal quantum computer, despite of entanglement in such devices, which we roughly estimate for the ideal case and for the harmful entanglement with photonic modes. We show that quasi-particles are the native shell for the entanglement already for ground state, in contast to the free electromagnetic field where vacuum state does not produce entanglement at all.

physics.gen-ph↗

arXiv2003

Limitation of computational resource as physical principle

Limitation of computational resources is considered as a universal principle that for simulation is as fundamental as physical laws are. It claims that all experimentally verifiable implications of physical laws can be simulated by the effective classical algorithms. It is demonstrated through a completely deterministic approach proposed for the simulation of biopolymers assembly. A state of molecule during its assembly is described in terms of the reduced density matrix permitting only limited tunneling. An assembly is treated as a sequence of elementary scatterings of simple molecules from the environment on the point of assembly. A decoherence is treated as a forced measurement of quantum state resulted from the shortage of computational resource. All results of measurements are determined by a choice from the limited number of special options of the nonphysical nature which stay unchanged till the completion of assembly; we do not use the random numbers generators. Observations of equal states during the assembly always give the same result. We treat a scenario of assembly as an establishing of the initial states for elementary scatterings. The different scenarios are compared according to the distributions of the assembly results.

quant-ph↗

arXiv2001

Quantum recognition of eigenvalues, structure of devices and thermodynamic properties

Quantum algorithms speeding up classical counterparts are proposed for the problems: 1. Recognition of eigenvalues with fixed precision. Given a quantum circuit generating unitary mapping $U$ and a complex number the problem is to determine is it an eigenvalue of $U$ or not. 2. Given a molecular structure find thermodynamic functions like partitioning function, entropy, etc. for a gas consisting of such molecules. 3. Recognition of molecular structures. Find a molecular structure given its spectrum. 4. Recognition of electronic devices. Given an electronic device that can be used only as a black box how to recognize its internal construction? We consider mainly structures generating sparse spectrums. These algorithms require the time from about square root to logarithm of the time of classical analogs and for the first three problems give exponential memory saving. Say, the time required for distinguishing two devices with the same given spectrum is about seventh root of the time of direct classical method, for the recognition of eigenvalue - about sixth root. Thus microscopic quantum devices can recognize molecular structures and physical properties of environment faster than big classical computers.

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