arXiv subjects

Lajos Diósi

Publications and source records attributed to Lajos Diósi.

At least 37 records · Page 2Linked to original sources

arXiv2022

Relativistic GKLS master equation?

The celebrated GKLS master equation, widely called just Lindblad equation, is the universal dynamical equation of non-relativistic open quantum systems in their Markovian approximation. It is not necessary and perhaps impossible that GKLS equations possess sensible relativistic forms. In a lucid talk on black hole information loss paradox, David Poulin conjectured a Lorentz invariant GKLS master equation. It remained unpublished. Poulin passed away at heights of his activity. But the equation is really puzzling. A closer look uncovers a smartly hidden defect which leaves us without Lorentz invariant Markovian master equations. They, in view of the present author, should not exist.

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arXiv2022

On the conjectured gravity-related collapse rate $E_Δ/\hbar$ of massive quantum superpositions

Roger Penrose and the author share the proposal that the spatial superposition $|x_1\rangle+|x_2\rangle$ of a massive object collapses into its localized components $|x_1\rangle$ or $|x_2\rangle$ with the characteristic time $\hbar/E_Δ$ where $E_Δ$ is the gravitational self-energy excess of the superposition versus the localized states. Underlying arguments of such radical departure from standard quantum mechanics and different derivations of the rate equation are briefly recapitulated and discussed.

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arXiv2022

MAQRO -- BPS 2023 Research Campaign Whitepaper

The objective of the proposed MAQRO mission is to harness space for achieving long free-fall times, extreme vacuum, nano-gravity, and cryogenic temperatures to test the foundations of physics in macroscopic quantum experiments. This will result in the development of novel quantum sensors and a means to probe the foundations of quantum physics at the interface with gravity. Earlier studies showed that the proposal is feasible but that several critical challenges remain, and key technologies need to be developed. These new technologies will open up the potential for achieving additional science objectives. The proposed research campaign aims to advance the state of the art and to perform the first macroscopic quantum experiments in space. Experiments on the ground, in micro-gravity, and in space will drive the proposed research campaign during the current decade to enable the implementation of MAQRO within the subsequent decade.

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arXiv2020

Decoherence and the puzzle of quantum Brownian motion in a gas

Heinz-Dieter Zeh's discovery that the motion of macroscopic objects can not, under typical conditions, follow the Schrödinger equation necessitates a suitably modified dynamics. This unfolded a long-lasting puzzle in the open quantum system context: what is the quantum counterpart of the classical Brownian motion in a gas. Presented is a criticism and an open-end discussion of the quantum linear Boltzmann and quantum Fokker-Planck equations -- with constant respect for foundational research.

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arXiv2019

Spontaneous Wave Function Collapse with Frame Dragging and Induced Gravity

I impose the Newtonian criteria of inertial frames on the c.o.m. trajectories of massive objects undergoing spontaneous collapse of their wave function. The corresponding modification of the so far used stochastic Schrödinger equation eliminates the Brownian motion of the c.o.m., restores the exact inertial motion for free masses. For the collapse of Schrödinger cat states the Born rule is satisfied invariably. The proposed machinery comes from the radical assumption that, in the vicinity of the spontaneously localized mass, the stochastic fluctuations of the c.o.m. ---inevitable in the collapse process--- would drag the physical inertial frame with themselves. The perspective of a general theory is presented where the spontaneous-collapse-caused breakdown of local energy-momentum conservation could be remedied by altering the metric, resulting in collapse-induced curvature of the space-time.

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arXiv2019

Nonlinear Schrödinger equation in foundations: summary of 4 catches

Fundamental modifications of the standard Schrödinger equation by additional nonlinear terms have been considered for various purposes over the recent decades. It came as a surprise when, inverting Abner Shimony's observation of "peaceful coexistence" between standard quantum mechanics and relativity, N. Gisin proved in 1990 that any (deterministic) nonlinear Schrödinger equation would allow for superluminal communication. This is by now the most spectacular and best known anomaly. We discuss further anomalies, simple but foundational, less spectacular but not less dramatic.

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arXiv2019

Two invariant surface-tensors determine CSL of massive body wave function

Decoherence of massive body wave function under Continuous Spontaneous Localization is reconsidered. It is shown for homogeneous probes with wave functions narrow in position and angle that decoherence is a surface effect. Corresponding new surface integrals are derived as the main result. Probe's constant density and two completely geometric surface-dependent invariant tensors encode full dependence of positional and angular decoherence of masses, irrespective of their microscopic structure. The two surface-tensors offer a new insight into CSL and a flexible approach to design laboratory test masses.

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arXiv2019

Planck length challenges non-relativistic quantum mechanics of large masses

With the simplest proof ever, we justify the significance of quantum-gravity in non-relativistic quantum mechanics together with the related theories and experiments. Since the de Broglie wave length is inverse proportional to the mass, it would descend towards and below the Planck scale 10^{-33} cm for large masses even at slow non-relativistic motion. The tricky relationship between gravity and quantum mechanics ---well-known in the relativistic case--- shows up in non-relativistic motion of massive objects. Hence the gravity-related modification of their Schrödinger equation is m a n d a t o r y. We also recall the option of an autonomous Newtonian quantum-gravity, a theory parametrized by hbar and G. On cancellation of c from the Newtonian limit of Planck scale metric fluctuations is given a new hint.

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arXiv2018

Continuous quantum measurement and Itô formalism

A new quantum-stochastic differential calculus is derived for representing continuous quantum measurement of the position operator. Closed nonlinear quantum-stochastic differential equation is given for the quantum state of the observed particle. Possible physical realization of continuous position measurement is constructed.

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arXiv2018

Normal ordering the squeeze operator by generalized Wick theorem

In 1988, I translated a popular article 'Squeezed light' for the Hungarian mutation of Scientific American. How shall we say 'squeezed' in our language from now on? At the time, Janszky was already Hungary's top quantum optics theorist, he excelled in squeezed light research as well, so I did not want to decide without asking him. He voted for the word 'préselt' [prayshalt], and it worked,became standard in our talking and writing about squeezed light. To his memory, let me dedicate an easy route (two pages) to normal ordering the squeeze operator, based on my recent extension of the Wick theorem for general orderings of q and p.

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arXiv2018

Wick theorem for all orderings of canonical operators

Wick's theorem, known for yielding normal ordered from time-ordered bosonic fields may be generalized for a simple relationship between any two orderings that we define over canonical variables, in a broader sense than before. In this broad class of orderings, the General Wick Theorem (GWT) follows from the Baker-Campbell-Hausdorff identity. We point out that, generally, the characteristic function does not induce an unambiguous scheme to order the multiple products of the canonical operators although the value of the ordered product is unique. We construct a manifold of different schemes for each value of s of s-orderings of Cahill and Glauber.

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arXiv2018

Fundamental Irreversibility: Planckian or Schrödinger-Newton?

The inception of a universal gravity-related irreversibility took place originally in quantum cosmology. The ultimate reason of universal irreversibility is thought to come from black holes close to the Planck scale. Completely different instances of irreversibilities are quantum state reductions unrelated to gravity or relativity but related to measurement devices. However, an intricate relationship between Newton gravity and quantized matter might result in fundamental and spontaneous quantum state reduction --- in the non-relativistic Schrödinger-Newton context. The above two concepts of fundamental irreversibility emerged and evolved with few or even no interactions. The purpose here is to draw a parallel between the two approaches first, and to ask rather than answer the question: can both the Planckian and the Schrödinger-Newton indeterminacies/irreversibilities be two faces of the same universe. A related personal note of the author's 1986 meeting with Aharonov and Bohm is appended.

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arXiv2018

How to teach and think about spontaneous wave function collapse theories: not like before

A simple and natural introduction to the concept and formalism of spontaneous wave function collapse can and should be based on textbook knowledge of standard quantum state collapse and monitoring. This approach explains the origin of noise driving the paradigmatic stochastic Schrödinger equations of spontaneous localization of the wave function $Ψ$. It reveals, on the other hand, that these equations are empirically redundant and the master equations of the noise-averaged state $\hatρ$ are the only empirically testable dynamics in current spontaneous collapse theories.

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arXiv2017

On GKLS dynamics for local operations and classical communication

We define a time continuous version of the concept of "local operations and classical communication" (LOCC), ubiquitous in quantum information theory. It allows us to construct GKLS master equations for particle systems that have (1) an arbitrary pair potential, and (2) local decoherence terms, but that do not entangle the constituents. The local decoherence terms take a particularly simple form if a principle of least decoherence is applied.

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arXiv2017

Principle of least decoherence for Newtonian semi-classical gravity

Recent works have proved that semi-classical theories of gravity needed not be fundamentally inconsistent, at least in the Newtonian regime. Using the machinery of continuous measurement theory and feedback, it was shown that one could construct well behaved models of hybrid quantum-classical dynamics at the price of an imposed (non unique) decoherence structure. We introduce a principle of least decoherence (PLD) which allows to naturally single out a unique model from all the available options; up to some unspecified short distance regularization scale. Interestingly, the resulting model is found to coincide with the old --erstwhile only heuristically motivated-- proposal of Penrose and one of us for gravity-related spontaneous decoherence and collapse. Finally, this letter suggests that it is in the submillimeter behavior of gravity that new phenomena might be found.

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arXiv2017

Equation of Motion for Estimation Fidelity of Monitored Oscillating Qubits

We study the convergence properties of state estimates of an oscillating qubit being monitored by a sequence of \textit{discrete}, unsharp measurements. Our method derives a differential equation determining the evolution of the estimation fidelity from a single incremental step. When the oscillation frequency $Ω$ is precisely known, the estimation fidelity converges exponentially fast to unity. For imprecise knowledge of $Ω$ we derive the asypmtotic estimation fidelity.

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arXiv2017

Notes on oldest jump unravelling of spatial decoherence master equation

Solution of free particle quantum master equation with spatial decoherence can be unravelled into stochastic quantum trajectories in many ways. The first example, published in 1985, proposed a piecewise deterministic jump process for the wave function. While alternative unravellings, diffusive ones in particular, proved to be tractable analytically, the jump process 1985, also called orthojump, allows for few analytic results, it needs numeric methods as well. Here we prove that, similarly to diffusive unravellings, it is localizing the quantum state.

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arXiv2017

Centre of mass decoherence due to time dilation: paradoxical frame-dependence

The recently proposed centre of mass decoherence of composite objects due to gravitational time-dilation [Pikovski et al., Nat.Phys. 15. June (2015); arXiv:1311.1095] is confronted with the principle of equivalence between gravity and observer's acceleration. In the laboratory frame, a positional superposition $\vert x_1\rangle+\vert x_2\rangle$ can quickly decohere whereas in the free-falling frame, as I argue, the superposition can survive for almost arbitrary long times. The paradoxical result is explained by the so far unappreciated feature of the proposed model: the centre of mass canonical subsystem is ambiguous, it is different in the laboratory and the free-falling frames, respectively. As long as the centre-of-mass motion of the composite object is non-relativistic, a simple Galilean-covariant Hamiltonian represents the Pikovski {\it et al} theory with exactly the same physical predictions. We emphasize the power of this Hamiltonian to understand essential features of the Pikovski {\it et al} theory and to moderate a few divergent statements in recent works.

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