# Publications

## Introductory quantum physics and relativity (Second edition)

, 2018

© 2018 by World Scientific Publishing Co. Pte. Ltd. All right reserved. This book is a revised and updated version of Introductory Quantum Physics and Relativity. Based on lectures given as part of the undergraduate degree programme at the University of Leeds, it has been extended in line with recent developments in the field. The book contains all the material required for quantum physics and relativity in the first three years of a traditional physics degree, in addition to more interesting and up-to-date extensions and applications which include quantum field theory, entanglement, and quantum information science. The second edition is unique as an undergraduate textbook as it combines quantum physics and relativity at an introductory level. It expounds the foundations of these two subjects in detail, but also illustrates how they can be combined. It discusses recent applications, but also exposes undergraduates to cutting-edge research topics, such as laser cooling, Bose-Einstein condensation, tunneling microscopes, lasers, nonlocality, and quantum teleportation.

## Operational effects of the UNOT gate on classical and quantum correlations

SCIENCE BULLETIN **63** (2018) 765-770

## Maximum one-shot dissipated work from Rényi divergences.

Physical review. E **97** (2018) 052135-052135

Thermodynamics describes large-scale, slowly evolving systems. Two modern approaches generalize thermodynamics: fluctuation theorems, which concern finite-time nonequilibrium processes, and one-shot statistical mechanics, which concerns small scales and finite numbers of trials. Combining these approaches, we calculate a one-shot analog of the average dissipated work defined in fluctuation contexts: the cost of performing a protocol in finite time instead of quasistatically. The average dissipated work has been shown to be proportional to a relative entropy between phase-space densities, to a relative entropy between quantum states, and to a relative entropy between probability distributions over possible values of work. We derive one-shot analogs of all three equations, demonstrating that the order-infinity Rényi divergence is proportional to the maximum possible dissipated work in each case. These one-shot analogs of fluctuation-theorem results contribute to the unification of these two toolkits for small-scale, nonequilibrium statistical physics.

## New ultra high-speed all-optical coherent D-trigger

Journal of Physics: Conference Series **1124** (2018)

© Published under licence by IOP Publishing Ltd. We study the interaction of two counterpropagating unipolar video pulses of electromagnetic radiation in a dense resonant two-level medium. The pulse durations are less than one oscillation period of an atomic transition. We show that a polariton cluster (i.e. the compact long-living strongly coupled state of electromagnetic field and matter polarisation) is created, when two unipolar video pulses collide in a resonant medium of the frequency ω o (the pulses correspond to self-induced transparency solitons of the same amplitudes and opposite polarities). We studied for the first time multiple recording and erasing of a polariton cluster in a thin layer of a resonant medium (quantum dots) placed on the mirror surface. We showed that dynamics of the medium population difference N(x,t) is analogous to the operation of a D-trigger of the pulse rate 60 000 GHz and higher. We found such a method of the polariton cluster recording and erasing that excludes the accumulation of erasing errors. Therefore, the total duration of the optical D-trigger operation time can strongly exceed the phase relaxation time T 2

## Squeezing Enhances Quantum Synchronization.

Physical review letters **120** (2018) 163601-163601

It is desirable to observe synchronization of quantum systems in the quantum regime, defined by the low number of excitations and a highly nonclassical steady state of the self-sustained oscillator. Several existing proposals of observing synchronization in the quantum regime suffer from the fact that the noise statistics overwhelm synchronization in this regime. Here, we resolve this issue by driving a self-sustained oscillator with a squeezing Hamiltonian instead of a harmonic drive and analyze this system in the classical and quantum regime. We demonstrate that strong entrainment is possible for small values of squeezing, and in this regime, the states are nonclassical. Furthermore, we show that the quality of synchronization measured by the FWHM of the power spectrum is enhanced with squeezing.

## Law and Disorder

New Scientist **237** (2018) 32-35

© 2018 Reed Business Information Ltd, England We are building machines to undermine nature's most rigid rule, says physicist Vlatko Vedral

## Causal Asymmetry in a Quantum World

PHYSICAL REVIEW X **8** (2018) ARTN 031013

## When can gravity path-entangle two spatially superposed masses?

PHYSICAL REVIEW D **98** (2018) ARTN 046001

## From micro to macro: Adventures of a wandering physicist

, 2018

© 2018 by World Scientific Publishing Co. Pte. Ltd. All rights reserved. This is a popular science book exploring the limits of scientific explanation. In particular, it debates if all sciences will ultimately be reducible to physics. The journey starts with physics itself, where there is a gap between the micro (quantum) and the macro (classical) and moves into chemistry, biology and the social sciences. Written by a practising scientist, this volume offers a personal perspective on various topics and incorporates the latest research.

## Quantum plug n' play: modular computation in the quantum regime

NEW JOURNAL OF PHYSICS **20** (2018) ARTN 013004

## Experimental Verification of a Jarzynski-Related Information-Theoretic Equality by a Single Trapped Ion.

Physical review letters **120** (2018) 010601-010601

Most nonequilibrium processes in thermodynamics are quantified only by inequalities; however, the Jarzynski relation presents a remarkably simple and general equality relating nonequilibrium quantities with the equilibrium free energy, and this equality holds in both the classical and quantum regimes. We report a single-spin test and confirmation of the Jarzynski relation in the quantum regime using a single ultracold ^{40}Ca^{+} ion trapped in a harmonic potential, based on a general information-theoretic equality for a temporal evolution of the system sandwiched between two projective measurements. By considering both initially pure and mixed states, respectively, we verify, in an exact and fundamental fashion, the nonequilibrium quantum thermodynamics relevant to the mutual information and Jarzynski equality.

## Entanglement between living bacteria and quantized light witnessed by rabi splitting

Journal of Physics Communications **2** (2018)

© 2018 The Author(s). We model recent experiments on living sulphur bacteria interacting with quantised light, using the Dicke model. Our analysis shows that the strong coupling between the bacteria and the light, when both are treated quantum-mechanically, indicates that in those experiments there is entanglement between the bacteria (modelled as dipoles) and the quantised light (modelled as a single quantum harmonic oscillator). The existence of lower polariton branch due to the vacuum Rabi splitting, measured in those experiments for a range of different parameters, ensures the negativity of energy (with respect to the lowest energy of separable states), thus acting as an entanglement witness.

## Quantum-gravity effects could in principle be witnessed in neutrino-like oscillations

NEW JOURNAL OF PHYSICS **20** (2018) ARTN 083011

## Operational one-to-one mapping between coherence and entanglement measures

PHYSICAL REVIEW A **96** (2017) ARTN 032316

## Gravitationally induced entanglement between two massive particles is sufficient evidence of quantum effects in gravity

Physical Review Letters American Physical Society **119** (2017)

All existing quantum-gravity proposals are extremely hard to test in practice. Quantum effects in the gravitational field are exceptionally small, unlike those in the electromagnetic field. The fundamental reason is that the gravitational coupling constant is about 43 orders of magnitude smaller than the fine structure constant, which governs light-matter interactions. For example, detecting gravitons—the hypothetical quanta of the gravitational field predicted by certain quantum-gravity proposals—is deemed to be practically impossible. Here we adopt a radically different, quantum-information-theoretic approach to testing quantum gravity. We propose witnessing quantumlike features in the gravitational field, by probing it with two masses each in a superposition of two locations. First, we prove that any system (e.g., a field) mediating entanglement between two quantum systems must be quantum. This argument is general and does not rely on any specific dynamics. Then, we propose an experiment to detect the entanglement generated between two masses via gravitational interaction. By our argument, the degree of entanglement between the masses is a witness of the field quantization. This experiment does not require any quantum control over gravity. It is also closer to realization than detecting gravitons or detecting quantum gravitational vacuum fluctuations.

## Witnessing the quantumness of a system by observing only its classical features

NPJ QUANTUM INFORMATION **3** (2017) ARTN 41

## Provably unbounded memory advantage in stochastic simulation using quantum mechanics

NEW JOURNAL OF PHYSICS **19** (2017) ARTN 103009

## Detecting metrologically useful asymmetry and entanglement by a few local measurements

PHYSICAL REVIEW A **96** (2017) ARTN 042327