In Print

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

My Research

Probing spectral features of quantum many-body systems with quantum simulators

The efficient probing of spectral features of quantum many-body systems is important for characterising and understanding the structure and dynamics of quantum materials. In this work, we establish a framework for probing the excitation spectrum of quantum many-body systems with quantum simulators. Our approach effectively realises a spectral detector by processing the dynamics of observables with time intervals drawn from a defined probability distribution, which only requires native time evolution governed by the Hamiltonian without any ancilla. The critical element of our method is the engineered emergence of frequency resonance such that the excitation spectrum can be probed. We show…

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Pionic Entanglement in Femtoscopy: A Lesson in Interference and Indistinguishability

We present an analysis of recent experiments in femtoscopy by the STAR collaboration in terms of the protocol of entanglement witnessing involving purity measurements. The entanglement is between the charge and momentum degrees of freedom of pions and the state purity measurements ultimately rely on the bosonic nature of the detected pions. The pion experiment is intended to measure the size of nuclei and the distance between the nuclei involved, however it indirectly confirms that the states of differently charged pions are entangled through an entanglement witness based on the purity of various pionic states. The entangled state of pions…

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Quantum Causal Inference with Extremely Light Touch

We consider the quantum version of inferring the causal relation between events. There has been recent progress towards identifying minimal interventions and observations needed. We here show, by means of constructing an explicit scheme, that quantum observations alone are sufficient for quantum causal inference for the case of a bipartite quantum system with measurements at two times. Our scheme involves the derivation of a closed-form expression for the space-time pseudo-density matrix associated with many times and qubits. This matrix can be determined by coarse-grained quantum observations alone. We show that from this matrix one can infer the causal structure via…

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The Everything-is-a-Quantum-Wave Interpretation of Quantum Physics

In this paper I would like to outline what I think is the most natural interpretation of quantum mechanics. By natural, I simply mean that it requires the least amount of excess baggage and that it is universal in the sense that it can be consistently applied to all the observed phenomena including the universe as a whole. I call it the “Everything is a Quantum Wave” Interpretation (EQWI) because I think this is a more appropriate name than the Many Worlds Interpretation (MWI). The paper explains why this is so.

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Entanglement in a qubit-qubit-tardigrade system

Quantum and biological systems are seldom discussed together as they seemingly demand opposing conditions. Life is complex, “hot and wet” whereas quantum objects are small, cold and well controlled. Here, we overcome this barrier with a tardigrade — a microscopic multicellular organism known to tolerate extreme physicochemical conditions via a latent state of life known as cryptobiosis. We observe coupling between the animal in cryptobiosis and a superconducting quantum bit and prepare a highly entangled state between this combined system and another qubit. The tomographic data shows entanglement in the qubit-qubit-tardigrade system, with the tardigrade modelled as an ensemble of…

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Unpredictability is perfectly possible in a deterministic universe

We revisit the vexed question of how unpredictability can arise in a deterministic universe, focusing on unitary quantum theory. We discuss why quantum unpredictability is irrelevant for the possibility of what some people call `free-will’, and why existing `free-will’ arguments are themselves irrelevant to argue for or against a physical theory.

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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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