In Print

A collection of my most cited research papers, and a selection of my books.

My Research

Conservation Laws Reveal the Quantumness of Gravity

Adopting a general framework for quantum-classical dynamics, we analyze the interaction between quantum matter and a classical gravitational field. We point out that, assuming conservation of momentum or energy, and assuming that the dynamics obeys a particular decomposition property set out in the paper, the classical gravitational field cannot change the momentum or energy of the quantum system, whereas the quantum gravitational field can do so. Drawing upon the fundamental relationship between conservation laws and the quantum properties of objects, our analysis offers new perspectives for the study of quantum gravity and provides a novel interpretation of existing experimental observations,…

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Comparing coherent and incoherent models for quantum homogenization

Here we investigate the role of quantum interference in the quantum homogenizer, whose convergence properties model a thermalization process. In the original quantum homogenizer protocol, a system qubit converges to the state of identical reservoir qubits through partial-swap interactions, that allow interference between reservoir qubits. We design an alternative, incoherent quantum homogenizer, where each system-reservoir interaction is moderated by a control qubit using a controlled-swap interaction. We show that our incoherent homogenizer satisfies the essential conditions for homogenization, being able to transform a qubit from any state to any other state to arbitrary accuracy, with negligible impact on the reservoir…

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Observable Thermalization: Theory, Numerical and Analytical Evidence

Predicting whether an observable will dynamically evolve to thermal equilibrium in an isolated quantum system is an important open problem, as it determines the applicability of thermodynamics and statistical mechanics. The Observable Thermalization framework has been proposed as a solution, characterizing observables that thermalize using an observable-specific maximum entropy principle. In this paper, we achieve three results. First, we confirm the dynamical relaxation of local observables towards maximum entropy, in a 1D Ising chain. Second, we provide the most general solution to the maximization problem and numerically verify some general predictions about equilibrium behavior in the same model. Third, we…

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Quantum mechanics with real numbers: entanglement, superselection rules and gauges

We show how imaginary numbers in quantum physics can be eliminated by enlarging the Hilbert Space followed by an imposition of – what effectively amounts to – a superselection rule. We illustrate this procedure with a qubit and apply it to the Mach-Zehnder interferometer. The procedure is somewhat reminiscent of the constrained quantization of the electromagnetic field, where, in order to manifestly comply with relativity, one enlargers the Hilbert Space by quantizing the longitudinal and scalar modes, only to subsequently introduce a constraint to make sure that they are actually not directly observable.

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Observing ghost entanglement beyond scattering amplitudes in quantum electrodynamics

A fully local quantum account of the interactions experienced between charges requires us to use all the four modes of the electromagnetic vector potential, in the Lorenz gauge. However, it is frequently stated that only the two transverse modes of the vector potential are “real” in that they contain photons that can actually be detected. The photons present in the other two modes, the scalar and the longitudinal, are considered unobservable, and are referred to as “virtual particles” or “ghosts”. Here we argue that this view is erroneous and that even these modes can, in fact, be observed. We present…

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Temporal witnesses of non-classicality in a macroscopic biological system

Exciton transfer along a polymer is essential for many biological processes, for instance light harvesting in photosynthetic biosystems. Here we apply a new witness of non-classicality to this phenomenon, to conclude that, if an exciton can mediate the coherent quantum evolution of a photon, then the exciton is non-classical. We then propose a general qubit model for the quantum transfer of an exciton along a polymer chain, also discussing the effects of environmental decoherence. The generality of our results makes them ideal candidates to design new tests of quantum features in complex bio-molecules.

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Visit the full research archive at Arxiv

My Books

Modern Foundations Of Quantum Optics
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Introductory Quantum Physics And Relativity
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Solid State Quantum Information
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Introduction to Quantum Information Science
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Decoding Reality
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From Micro to Macro
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My Blog

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Entropic Forces

This mysteriously sounding concept is widely used in biology. The chief reason being that life, in fact, is a struggle against the Second Law of thermodynamics.

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Crazy Quantum (Late-Night) Thoughts

The main obstacle to us making progress in quantum physics is the persistent (and misplaced) belief that quantum physics needs to be fixed.

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What is a Q-Field?

I have frequently talked about the interpretation of quantum physics implying that “everything is a quantum wave”. Here I’d like to explain this a bit better and, more importantly, tell you about some problems with this picture of the universe.

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