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Bogusław Broda

Publications and source records attributed to Bogusław Broda.

At least 19 recordsLinked to original sources
arXiv2024

Unitary (semi)causal quantum-circuit representation of black hole evaporation

A general structure of unitary evolution (evaporation) of the black hole, respecting causality imposed by the event horizon (semicausality), has been derived and presented in the language of quantum circuits. The resulting consequences for the evolution of the corresponding entanglement entropy and the entropy curve have been determined. As an illustration of the general scheme, two families of qubit toy models have been discussed: tensor product models and controlled non-product models.

gr-qc↗
arXiv2021

Causal unitary qubit model of black hole evaporation

A new simple qubit model of black hole evaporation is proposed. The model operates on four qubits and is defined in terms of quantum gates and a quantum circuit. The chief features of the model include explicit unitarity and (most notably) causality which is understood as the impossibility of the transfer of information from the interior of the black hole through its horizon. The corresponding von Neumann entanglement entropy yields a crude (four-qubit) approximation of the Page curve.

quant-ph↗
arXiv2021

Fermionic model of unitary transport of qubits from a black hole

Inspired by a recent model of Osuga and Page, we propose an explicitly unitary fermionic toy model for transferring information from a black hole to the outgoing radiation. The model treats the unitary evolution as a composition of the Hawking pair creation outside the black hole and of pair annihilation inside the black hole.

hep-th↗
arXiv2020

Unitary toy qubit transport model for black hole evaporation

In a recent paper Osuga and Page have presented an explicitly unitary toy qubit transport model for transferring information from a black hole to the outgoing radiation. Following their idea we propose a unitary toy model which involves (fermionic) Hawking states.

hep-th↗
arXiv2020

Total spectral distributions from Hawking radiation

Taking into account time-dependence of the Hawking temperature and finite evaporation time of the black hole, total spectral distributions of the radiant energy and of the number of particles have been explicitly calculated and compared to their temporary (initial) blackbody counterparts (spectral exitances).

gr-qc↗
arXiv2020

Unitary evolution to a state with a fixed mean number of particles

In the framework of finite-dimensional Fock space models, for a predefined fixed mean number of particles $\bar{n}_{k}$, it is shown that there is a ``large'' multi-dimensional subspace $s_{\bar{n}_{k}}$ of initial pure states, in the space $S$ of all pure states, unitarily evolving to a subspace $S_{\bar{n}_{k}}$ of final pure states which yield $\bar{n}_{k}$. As an example, in particular it follows that the blackbody form of the mean number of particles $\bar{n}_{k}$ does not by itself contradict unitarity of black hole evaporation.

gr-qc↗
arXiv2015

Quantum search of a real unstructured database

A simple circuit implementation of the oracle for Grover's quantum search of a real unstructured classical database is proposed. The oracle contains a kind of quantumly accessible classical memory, which stores the database.

quant-ph↗
arXiv2015

One-loop contribution to the matter-driven expansion of the Universe

Standard perturbative quantum gravity formalism is applied to compute the lowest order corrections to the spatially flat cosmological FLRW solution governed by ordinary matter. The presented approach is analogous to the one used to compute quantum corrections to the Coulomb potential in electrodynamics, or to the approach applied in computation of quantum corrections to the Schwarzschild solution in gravity. In this framework, it is shown that the corrections to the classical metric coming from the one-loop graviton vacuum polarization (self-energy) have (UV cutoff dependent) repulsive properties, which could be not negligible in the very early Universe.

gr-qc↗
arXiv2013

Perturbative quantum damping of cosmological expansion

Perturbative quantum gravity in the framework of the Schwinger-Keldysh formalism is applied to compute lowest-order corrections to the actual expansion of the Universe described in terms of the spatially flat Friedman-Lematre-Robertson-Walker solution. The classical metric is approximated by a third order polynomial perturbation around the Minkowski metric. It is shown that the quantum contribution to the classical expansion, although extremely small, has damping properties (quantum friction), i.e. it slows down the expansion.

hep-th↗
arXiv2012

"Microscopic" approach to the Ricci dark energy

A derivation of the Ricci dark energy from quantum field theory of fluctuating "matter" fields in a classical gravitational background is presented. The coupling to the dark energy, the parameter 'a', is estimated in the framework of our formalism, and qualitatively it appears to be within observational expectations.

gr-qc↗
arXiv2012

Vacuum pressure, dark energy and dark matter

It has been argued that the correct, i.e. positive, sign of quantum vacuum energy density, or more properly, negative sign of quantum vacuum pressure, requires not a very large number, e.g. ~100, of additional, undiscovered fundamental bosonic particle species, absent in the standard model. Interpretation of the new particle species in terms of dark matter ones permits to qualitatively, and even quantitatively, connect all the three concepts given in the title.

gr-qc↗
arXiv2011

An OPERA inspired classical model reproducing superluminal velocities

In the context of the sensational results concerning superluminal velocities, announced recently by the OPERA Collaboration, we have proposed a classical model yielding a statistically calculated measured velocity of a beam, higher than the velocity of the particles constituting the beam. The two key elements of our model, necessary and sufficient to obtain this curious result, are a time-dependent "transmission" function and statistical method of the maximum-likelihood estimation.

physics.data-an↗
arXiv2011

Quantum gravity stability of isotropy in homogeneous cosmology

It has been shown that anisotropy of homogeneous spacetime described by the general Kasner metric can be damped by quantum fluctuations coming from perturbative quantum gravity in one-loop approximation. Also, a formal argument, not limited to one-loop approximation, is put forward in favor of stability of isotropy in the exactly isotropic case.

gr-qc↗
arXiv2011

On possible violation of the CHSH Bell inequality in a classical context

It has been shown that there is a small possibility to experimentally violate the CHSH Bell inequality in a 'classical' context. The probability of such a violation has been estimated in the framework of a classical probabilistic model in the language of a random-walk representation.

quant-ph↗
arXiv2011

One-loop quantum gravity repulsion in the early Universe

Perturbative quantum gravity formalism is applied to compute the lowest order corrections to the classical spatially flat cosmological FLRW solution (for the radiation). The presented approach is analogous to the approach applied to compute quantum corrections to the Coulomb potential in electrodynamics, or rather to the approach applied to compute quantum corrections to the Schwarzschild solution in gravity. In the framework of the standard perturbative quantum gravity, it is shown that the corrections to the classical deceleration, coming from the one-loop graviton vacuum polarization (self-energy), have (UV cutoff free) opposite to the classical repulsive properties which are not negligible in the very early Universe. The repulsive "quantum forces" resemble those known from loop quantum cosmology.

gr-qc↗
arXiv2010

Induced gauge interactions revisited

It has been shown that the old-fashioned idea of Sakharov's induced gravity and gauge interactions in the "one-loop dominance" version works astonishingly well yielding reasonable parameters. It appears that induced coupling constants of gauge interactions of the standard model assume qualitatively realistic values. Moreover, it is possible to induce the Barbero--Immirzi parameter of canonical gravity from the fields entering the standard model.

hep-th↗