arXiv subjects

Antony Valentini

Publications and source records attributed to Antony Valentini.

44 records · Page 3Linked to original sources

arXiv2004

Extreme Test of Quantum Theory with Black Holes

We propose an extreme test of quantum theory using astrophysical black holes and entangled photons from atomic cascades. The identification of a cascade emission close to a black-hole event horizon would allow us to observe photons entangled with partners that have fallen behind the horizon. The experiment involves testing the characteristic cos^2(theta) modulation of photon transmission through a pair of polarisers at relative angle theta (Malus' law). For single photons, Malus' law is a remarkable feature of quantum theory: it is equivalent to expectation additivity for incompatible observables, and is generically violated for hidden-variables theories with nonstandard probability distributions. An experiment with entangled states straddling an event horizon is motivated by the Hawking information loss puzzle, as well as on general grounds. In principle, one could test the currently observed X-ray photons in iron lines from black-hole accretion discs. However, only a small fraction (~0.6%) have cascade partners, and current X-ray polarimetry does not permit successive measurements on a single X-ray photon. A realisable experiment requires the identification of an appropriate cascade in a more convenient frequency band.

astro-ph↗

arXiv2004

Black Holes, Information Loss, and Hidden Variables

We consider black-hole evaporation from a hidden-variables perspective. It is suggested that Hawking information loss, associated with the transition from a pure to a mixed quantum state, is compensated for by the creation of deviations from Born-rule probabilities outside the event horizon. The resulting states have non-standard or 'nonequilibrium' distributions of hidden variables, with a specific observable signature - a breakdown of the sinusoidal modulation of quantum probabilities for two-state systems. Outgoing Hawking radiation is predicted to contain statistical anomalies outside the domain of the quantum formalism. Further, it is argued that even for a macroscopic black hole, if one half of an entangled EPR-pair should fall behind the event horizon, the other half will develop similar statistical anomalies. We propose a simple rule, whereby the relative entropy of the nonequilibrum (hidden-variable) distribution generated outside the horizon balances the increase in von Neumann entropy associated with the pure-to-mixed transition. It is argued that there are relationships between hidden-variable and von Neumann entropies even in non-gravitational physics. We consider the possibility of observing anomalous polarisation probabilities, in the radiation from primordial black holes, and in the atomic cascade emission of entangled photon pairs from black-hole accretion discs.

hep-th↗

arXiv2004

Dynamical Origin of Quantum Probabilities

We study the origin of the Born probability rule rho = |psi|^2 in the de Broglie-Bohm pilot-wave formulation of quantum theory. It is argued that quantum probabilities arise dynamically, and have a status similar to thermal probabilities in ordinary statistical mechanics. This is illustrated by numerical simulations for a two-dimensional system. We show that a simple initial ensemble with a non-standard distribution rho not= |psi|^2 of particle positions evolves towards the quantum distribution to high accuracy. The relaxation process rho --> |psi|^2 is quantified in terms of a coarse-grained H-function (equal to minus the relative entropy of rho with respect to |psi|^2), which is found to decrease approximately exponentially over time, with a time constant that accords with a simple theoretical estimate.

quant-ph↗

arXiv2003

Universal Signature of Non-Quantum Systems

It is shown that 'non-quantum systems', with anomalous statistical properties, would carry a distinctive experimental signature. Such systems can exist in deterministic hidden-variables theories (such as the pilot-wave theory of de Broglie and Bohm). The signature consists of non-additive expectations for non-commuting observables, breaking the sinusoidal modulation of quantum probabilities for two-state systems. This effect is independent of the quantum state (pure or mixed), or of the details of the hidden-variables model. Experiments are proposed, testing polarisation probabilities for single photons.

quant-ph↗

arXiv2002

Subquantum Information and Computation

It is argued that immense physical resources - for nonlocal communication, espionage, and exponentially-fast computation - are hidden from us by quantum noise, and that this noise is not fundamental but merely a property of an equilibrium state in which the universe happens to be at the present time. It is suggested that 'non-quantum' or nonequilibrium matter might exist today in the form of relic particles from the early universe. We describe how such matter could be detected and put to practical use. Nonequilibrium matter could be used to send instantaneous signals, to violate the uncertainty principle, to distinguish non-orthogonal quantum states without disturbing them, to eavesdrop on quantum key distribution, and to outpace quantum computation (solving NP-complete problems in polynomial time).

quant-ph↗

arXiv2002

Signal-Locality in Hidden-Variables Theories

We prove that all deterministic hidden-variables theories, that reproduce quantum theory for a 'quantum equilibrium' distribution of hidden variables, predict the existence of instantaneous signals at the statistical level for hypothetical 'nonequilibrium ensembles'. This signal-locality theorem generalises yet another property of the pilot-wave theory of de Broglie and Bohm. The theorem supports the hypothesis that in the remote past the universe relaxed to a state of statistical equilibrium (at the hidden-variable level) in which nonlocality happens to be masked by quantum noise.

quant-ph↗

arXiv2001

Signal-Locality and Subquantum Information in Deterministic Hidden-Variables Theories

It is proven that any deterministic hidden-variables theory, that reproduces quantum theory for a 'quantum equilibrium' distribution of hidden variables, must predict the existence of instantaneous signals at the statistical level for hypothetical 'nonequilibrium ensembles'. This 'signal-locality theorem' generalises yet another feature of the pilot-wave theory of de Broglie and Bohm, for which it is already known that signal-locality is true only in equilibrium. Assuming certain symmetries, lower bounds are derived on the 'degree of nonlocality' of the singlet state, defined as the (equilibrium) fraction of outcomes at one wing of an EPR-experiment that change in response to a shift in the distant angular setting. It is shown by explicit calculation that these bounds are satisfied by pilot-wave theory. The degree of nonlocality is interpreted as the average number of bits of 'subquantum information' transmitted superluminally, for an equilibrium ensemble. It is proposed that this quantity might provide a novel measure of the entanglement of a quantum state, and that the field of quantum information would benefit from a more explicit hidden-variables approach. It is argued that the signal-locality theorem supports the hypothesis, made elsewhere, that in the remote past the universe relaxed to a state of statistical equilibrium at the hidden-variable level, a state in which nonlocality happens to be masked by quantum noise.

quant-ph↗

arXiv2001

Hidden Variables, Statistical Mechanics and the Early Universe

It is argued that our universe happens to be in a state of statistical equilibrium at the hidden-variable level, such that nonlocality is masked by quantum noise. To account for this 'quantum equilibrium', we outline a subquantum statistical mechanics in configuration space, and an H-theorem analogous to the classical coarse-graining H-theorem. Foundational issues in statistical mechanics are addressed, and an alternative explanation based on 'typicality' is criticised. An estimate is given for the relaxation timescale, and an illustrative numerical simulation is provided. Assuming the universe began in quantum non-equilibrium, we sketch a scenario in which relaxation is suppressed at very early times by the rapid expansion of space, raising the possibility that deviations from quantum theory could survive to the present day for relic cosmological particles that decoupled sufficiently early. It is concluded that quantum noise is a remnant of the big bang and, like the microwave background, should be probed experimentally. Possible tests with relic particles are briefly discussed.

quant-ph↗