# 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.

## Causal Asymmetry in a Quantum World

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

## Evolution without evolution and without ambiguities

PHYSICAL REVIEW D **95** (2017) ARTN 043510

## Local reversibility and entanglement structure of many-body ground states

QUANTUM SCIENCE AND TECHNOLOGY **2** (2017) UNSP 015005

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

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

## Device-Independent Tests of Quantum Measurements.

Physical review letters **118** (2017) 250501-250501

We consider the problem of characterizing the set of input-output correlations that can be generated by an arbitrarily given quantum measurement. Our main result is to provide a closed-form, full characterization of such a set for any qubit measurement, and to discuss its geometrical interpretation. As applications, we further specify our results to the cases of real and complex symmetric, informationally complete measurements and mutually unbiased bases of a qubit, in the presence of isotropic noise. Our results provide the optimal device-independent tests of quantum measurements.

## Gravitationally Induced Entanglement between Two Massive Particles is Sufficient Evidence of Quantum Effects in Gravity.

Physical review letters **119** (2017) 240402-

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.

## Using quantum theory to simplify input-output processes

NPJ QUANTUM INFORMATION **3** (2017) ARTN 6

## Why we need to quantise everything, including gravity

NPJ QUANTUM INFORMATION **3** (2017) ARTN 29

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

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

## Universal upper bounds on the Bose-Einstein condensate and the Hubbard star

PHYSICAL REVIEW B **96** (2017) ARTN 064502

## Influence of the fermionic exchange symmetry beyond Pauli's exclusion principle

PHYSICAL REVIEW A **95** (2017) ARTN 022336

## No-Hypersignaling Principle.

Physical review letters **119** (2017) 020401-020401

A paramount topic in quantum foundations, rooted in the study of the Einstein-Podolsky-Rosen (EPR) paradox and Bell inequalities, is that of characterizing quantum theory in terms of the spacelike correlations it allows. Here, we show that to focus only on spacelike correlations is not enough: we explicitly construct a toy model theory that, while not contradicting classical and quantum theories at the level of spacelike correlations, still displays an anomalous behavior in its timelike correlations. We call this anomaly, quantified in terms of a specific communication game, the "hypersignaling" phenomena. We hence conclude that the "principle of quantumness," if it exists, cannot be found in spacelike correlations alone: nontrivial constraints need to be imposed also on timelike correlations, in order to exclude hypersignaling theories.

## Witness gravity's quantum side in the lab.

Nature **547** (2017) 156-158

## A Nanophotonic Structure Containing Living Photosynthetic Bacteria.

Small (Weinheim an der Bergstrasse, Germany) **13** (2017)

Photosynthetic organisms rely on a series of self-assembled nanostructures with tuned electronic energy levels in order to transport energy from where it is collected by photon absorption, to reaction centers where the energy is used to drive chemical reactions. In the photosynthetic bacteria Chlorobaculum tepidum, a member of the green sulfur bacteria family, light is absorbed by large antenna complexes called chlorosomes to create an exciton. The exciton is transferred to a protein baseplate attached to the chlorosome, before migrating through the Fenna-Matthews-Olson complex to the reaction center. Here, it is shown that by placing living Chlorobaculum tepidum bacteria within a photonic microcavity, the strong exciton-photon coupling regime between a confined cavity mode and exciton states of the chlorosome can be accessed, whereby a coherent exchange of energy between the bacteria and cavity mode results in the formation of polariton states. The polaritons have energy distinct from that of the exciton which can be tuned by modifying the energy of the optical modes of the microcavity. It is believed that this is the first demonstration of the modification of energy levels within living biological systems using a photonic structure.

## 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

## Thermodynamics of complexity and pattern manipulation.

Physical review. E **95** (2017) 042140-042140

Many organisms capitalize on their ability to predict the environment to maximize available free energy and reinvest this energy to create new complex structures. This functionality relies on the manipulation of patterns-temporally ordered sequences of data. Here, we propose a framework to describe pattern manipulators-devices that convert thermodynamic work to patterns or vice versa-and use them to build a "pattern engine" that facilitates a thermodynamic cycle of pattern creation and consumption. We show that the least heat dissipation is achieved by the provably simplest devices, the ones that exhibit desired operational behavior while maintaining the least internal memory. We derive the ultimate limits of this heat dissipation and show that it is generally nonzero and connected with the pattern's intrinsic crypticity-a complexity theoretic quantity that captures the puzzling difference between the amount of information the pattern's past behavior reveals about its future and the amount one needs to communicate about this past to optimally predict the future.

## Entropic equality for worst-case work at any protocol speed

NEW JOURNAL OF PHYSICS **19** (2017) ARTN 043013

## Organic molecule fluorescence as an experimental test-bed for quantum jumps in thermodynamics.

Proceedings. Mathematical, Physical, and Engineering Sciences **473** (2017) 20170099-

We demonstrate with an experiment how molecules are a natural test bed for probing fundamental quantum thermodynamics. Single-molecule spectroscopy has undergone transformative change in the past decade with the advent of techniques permitting individual molecules to be distinguished and probed. We demonstrate that the quantum Jarzynski equality for heat is satisfied in this set-up by considering the time-resolved emission spectrum of organic molecules as arising from quantum jumps between states. This relates the heat dissipated into the environment to the free energy difference between the initial and final state. We demonstrate also how utilizing the quantum Jarzynski equality allows for the detection of energy shifts within a molecule, beyond the relative shift.