In Print

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

My Research

Are There Any Real Problems With Quantum Gravity?

We present a short, general and accessible introduction to quantizing gravity in the Heisenberg picture. We then apply this formalism to the scenario where two spatially superposed masses interact through the gravitational field. We discuss some of the consequences for quantum gravity including the spin of the graviton, the notions of locality and causality, as well as going beyond the linear regime. We use the Schwinger action principle and the Heisenberg representation which we believe make the issues involved clearer. We conclude by commenting on a number of traditionally discussed apparent problems with quantizing gravity (only to, ultimately, deny their…

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Classical Evolution Without Evolution

The well known argument of Page and Wootters demonstrates how to “derive” the usual quantum dynamics of a subsystem in a global state which is an eigenstate of the total Hamiltonian. I show how the same argument can be made in classical physics, by using a formalism that closely resembles the quantum one. This is not surprising since the Hamilton-Jacobi formulation of classical dynamics is precisely motivated by the logic of timeless dynamics. Ultimately, the key to obtaining dynamics without dynamics is the principle of energy conservation which leads to correlations between times pertaining to different subsystems. The same can,…

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Amplification of Gravitationally Induced Entanglement

Observation of gravitationally induced entanglement between two massive particles is the evidence of quantum nature of gravity. However, quantum effects in the gravitational field are exceptionally small so that the existing quantum-gravity proposals are extremely hard to test in practice. For addressing this key challenge, here we propose a criterion based on the logical contradictions of weak entanglement, which may boost the sensitivity of the signal due to the gravitationally induced entanglement. Specifically, we make use of the weak-value scenario and Einstein-Podolsky-Rosen (EPR) steering. We prove that it is impossible for a classical mediator to act on two local quantum…

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Quantum cooling activated by coherent-controlled thermalisation

In this paper, we show that by applying N identical thermalizing channels in a superposition of N cyclic causal orders [2], one can largely boost the heat extracting ability of the working system in ICO fridge even in the ultracold regime (it can be further boosted by utilizing a quDit working system in low temperature region). Moreover, in the controlled-SWAP scheme first introduced in [1] where we have access to the reservoir qubits which are quantum correlated with the control-target system, the performance of the fridge can be greatly enhanced in general(tripled for all N’s and temperatures). Then inspired by [3,4], we…

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A local-realistic theory for fermions

We propose a local model for general fermionic systems, which we express in the Heisenberg picture. To this end, we shall use a recently proposed formalism, the so-called “Raymond-Robichaud” construction, which allows one to construct an explicitly local model for any dynamical theory that satisfies no-signalling, in terms of equivalence classes of transformations that can be attached to each individual subsystem. By following the rigorous use of the parity superselection rule for fermions, we show how this construction removes the usual difficulties that fermionic systems display in regard to the definition of local states and local transformations.

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A Microscopic Quantum Model For the Experiment Coupling Qubits to a Tardigrade

We provide a quantum model for the recent experiment coupling a tardigrade to superconducting qubits. A number of different perspectives are discussed with the emphasis placed on quantum entanglement between different subsystems involved in the description.

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Spin, Statistics, Spacetime and Quantum Gravity

We explore the possibility that the connection between spin and statistics in quantum physics is of dynamical origin. We suggest that the gravitational field could provide a fully local mechanism for the phase that arises when fermionic and bosonic particles are exchanged. Our results hold even if the symmetry of space and time is Galilean, thus establishing that special relativity is not needed to explain the existence of spin (although it does motivate the introduction of creation and annihilation of particles, but this is a separate issue). We provide a model for the coupling between a particle of general spin…

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A Classical (Local) Account of The Aharonov-Bohm Effect

It is frequently stated that the electromagnetic vector potential acquires a fundamental role in quantum physics, whereas classically it only represents a convenient, but by no means necessary, way of representing the electromagnetic field. Here we argue that this is a historical accident due to the fact that the electromagnetic field was discovered before photons, while the electron itself was discovered first as a particle, before it became clear that it must also be treated as a wave and therefore as an excitation of the underlying electron field. We illustrate the fact that the vector potential ought to play a…

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Quantum Signatures of Gravity from Superpositions of Primordial Massive Particles

We study the superposition of primordial massive particles and compute the associated decoherence time scale in the radiation dominated universe. We observe that for lighter primordial particles with masses up to 107kg, the corresponding decoherence time scale is significantly larger than the age of the observable universe, demonstrating that a primordial particle would persist in a pure quantum state, with its wavefunction spreading freely. For heavier particles, they can still be in a quantum state while their position uncertainties are limited by the wavelength of background photons. We then discuss three observational signatures that may arise from a quantum superposition of…

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Jordan in The Church of The Higher Hilbert Space: Entanglement and Thermal Fluctuations

I revisit Jordan’s derivation of Einstein’s formula for energy fluctuations in the black body in thermal equilibrium. This formula is usually taken to represent the unification of the wave and the particle aspects of the electromagnetic field since the fluctuations can be shown to be the sum of wave-like and particle-like contributions

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Classical and Quantum Orbital Correlations in the Molecular Electronic States

The quantum superposition principle has been extensively utilized in the quantum mechanical description of the bonding phenomenon. It explains the emergence of delocalized molecular orbitals and provides a recipe for the construction of near-exact electronic wavefunctions. On the other hand, its existence in composite systems may give rise to nonclassical correlations that are regarded now as a resource in quantum technologies. Here, we approach the electronic ground states of three prototypical molecules from the point of view of fermionic information theory. For the first time in the literature, we properly decompose the pairwise orbital correlations into their classical and quantum…

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Refrigeration with Indefinite Causal Orders on a Cloud Quantum Computer

We demonstrate non-classical cooling on the IBMq cloud quantum computer. We implement a recently proposed refrigeration protocol which relies upon indefinite causal order for its quantum advantage. We use quantum channels which, when used in a well-defined order, are useless for refrigeration. We are able to use them for refrigeration, however, by applying them in a superposition of different orders. Our protocol is by nature relatively robust to noise, and so can be implemented on this noisy platform. As far as the authors are aware, this is the first example of cloud quantum refrigeration.

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Visit the full research archive at Arxiv

My Books

Portals to a New Reality: Five Pathways to the Future of Physics
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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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My Blog

Substack

Only the soul gets teleported

One of the inventors of quantum teleportation, the late Israeli physicist Asher Peres, was once asked by a journalist if a human being was to be quantum teleported, “Would the whole being be teleported with the soul or only the body?” His witty reply was: “No, only the soul gets teleported!”

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Flat Qubiters

Flat Earthers are a small but growing community of people who, as the name suggests, believe that the Earth is flat. They claim, despite overwhelming evidence to the contrary, that they can account using flat geometry for all the experiments revealing the Earth’s spherical shape.

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Macroscopic Quantum Entanglement

The discovery of quantum mechanics in 1925 was followed by a fierce debate about its meaning and implications. And this debate still rages on, but there have been many twists and turns since the early days. This blog is about the twists that I think are about to happen.

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