David Edward Bruschi

In the past few years, advances in quantum thermodynamics have shown that work can be stored in the quantum correlations of a state. A thermal state is the most entropic state one can prepare given a fixed amount of energy. However, with the same amount of energy, one can prepare a state with some entanglement, which can be used in clever protocols to perform for, i.e., to "store energy".

If this is true, entanglement should have a weight, since we have known for more than a century that energy has a weight.

I have worked on answering a preliminary question, which could set a challenge and a direction of research [1]: understanding which type of entanglement weighs, and why.

I have mainly contributed to this field by introducing and developing techniques to treat mode entanglement of modes within one or two cavities. I have shown, mainly together with my colleagues at Nottingham, that when one cavity moves, entanglement between the modes of a quantum field is affected and can be degraded, preserved or created. I have provided the techniques to fully characterized the phenomena that occurred in such localized systems. My results have attracted the interest of experimental scientists and we are now looking at possible experimental proposals.

A recent avenue that has been proposed by myself and collaborators investigates how to employ localized detectors, modeled by harmonic oscillators, for tasks that are typically investigated with Unruh-deWitt detectors. Unruh-deWitt detectors require perturbation theory which, a part from mathematical challenges, does not provide a full understanding on the physics under investigation. We have shown that, contrary to setups involving Unruh-deWitt, it is possible to employ this new scheme to analytically solve the time evolution of interacting quantum systems.

It is still an open question which are the effects, if any, of space-time curvature and gravity on quantum physics at large scales i.e., the scales at which relativity becomes important. Space agencies across the world are interested in bringing quantum technologies, such as quantum key distribution (QKD), to space!

QKD explains how you and I can exchange information and make sure that only the two of us can access it. In addition, we would like to know if somebody is messing around with the information we are exchanging. QKD offers a recipe, based on quantum mechanics, which allows us to do this! What we need to do is share a secret*key*, which allows us (and only us) to encode and decode any information we exchange. There are clever protocols which allow us to share the secret key (the original BB84 is described in [5]) and there are companies that now sell technology based on these principles!

Furthermore, ICT roadmaps of different countries envision that going to space is the future for quantum (and perhaps relativistic?) technologies [6]!

I have investigated the effects of gravity on quantum communication schemes. The research was partly inspired by [7]. I was able to show that if a user on the earth tries to exchange a secret key with a user on a spaceship, for example the International Space Station (ISS), the key will be affected by the curvature of space-time around the earth and these effects are measurable with current technology!

Furthermore, we have shown that by employing relativistic quantum metrology, one can aim at exploiting the effects described above for ultra-precise measurements of relevant parameters, such as distances in a future quantum GPS.

QKD explains how you and I can exchange information and make sure that only the two of us can access it. In addition, we would like to know if somebody is messing around with the information we are exchanging. QKD offers a recipe, based on quantum mechanics, which allows us to do this! What we need to do is share a secret

Furthermore, ICT roadmaps of different countries envision that going to space is the future for quantum (and perhaps relativistic?) technologies [6]!

I have investigated the effects of gravity on quantum communication schemes. The research was partly inspired by [7]. I was able to show that if a user on the earth tries to exchange a secret key with a user on a spaceship, for example the International Space Station (ISS), the key will be affected by the curvature of space-time around the earth and these effects are measurable with current technology!

Furthermore, we have shown that by employing relativistic quantum metrology, one can aim at exploiting the effects described above for ultra-precise measurements of relevant parameters, such as distances in a future quantum GPS.

A very basic question naturally arises: can thermodynamics can be exported to single (and small) systems?

The answer is

This has led many scientists to work in the area pf physics loosely named quantum thermodynamics. The aim is to understand how to extend concepts such as heat, work and temperature to systems with one or few constituents.

I have recently applied state of the art tools from quantum thermodynamics to relativistic fields, such as bosons and fermions. The results are very interesting because it is still not well understood what is the interplay between relativity, quantum correlations, energy and entropy. One can show that quantum correlations come at a cost, and we try to understand how this cost depends on the relativistic nature of the fundamental constituents of our universe.

Together with my collaborators, I found the ultimate bound on how many correlations can be created given a fixed amount of work that can be used in a unitary process. This will help me develop more the quantum thermodynamics of relativistic systems.

Ten years later, it was shown by Bill Unruh that systems that can be realized in the laboratory (i.e., flowing water tanks) can be manipulated to exhibit regimes where small perturbations (i.e., surface ripples) propagate as if on a curved space-time and in the presence of a black hole [9]. This opened a huge avenue opportunities, namely the possibility of testing Hawking's prediction in systems that are experimentally accessible so far (nobody has volunteered to fall in a black hole to see what happens, never being able to come back out and tell us what they witnessed...). In particular, new systems were found that could be led to exhibit these regimes, for example light wave guides and Bose-Einstein Condensates (BECs); these systems are now commonly employed in laboratories across the globe to study features typical of gravitational processes.

Great progress has been made and analogue radiation from analogue black holes has been observed. However, its most prominent feature, the quantum character of the correlations trademark of this radiation, are hard to be observed.

I have contributed to this area of research by providing a simple analytical understanding of the role of the initial temperature of the system that is being used (temperature that can never be brought to zero) and how this affects the correlations in the analogue radiation. My work is the first to give the experimental groups a temperature threshold above which no matter how good they are, they cannot observe quantum correlations.

- "On the wight of entanglement", D. E. Bruschi, Physics Letters B 54: 182-186 (2016)
- "Alice falls into a black hole", I. Fuentes-Schuller and R. Mann, Physical Review Letters 95: 120404 (2005)
- "Lorentz Invariance of Entanglement", P. M. Alsing, G. J. Milburn, arXiv:quant-ph/0203051v1 (2002)
- "Quantum Entropy", A. Peres, P. F. Scudo, D. R. Terno, Physical Review Letters 88: 230402 (2002)
- "Notes on black-hole evaporation". W.G. Unruh, Physical Review D 14 (4): 870 (1976)
- "Quantum Cryptography: Public key distribution and coin tossing", C. H. Bennett and G. Brassard, Proceedings of the IEEE International Conference on Computers, Systems, and Signal Processing, Bangalore, p. 175 (1984)
- Quantum Information and Communication European roadmap: http://qurope.eu/projects/quie2t/wp2/deliverables;

Roadmap of Quantum ICT Laboratory of National Institute of Information and Communications Technology of Japan: http://www.nict.go.jp/en/advanced\_ict/quantum/roadmap.html;

Quantum Information Science and Technology Roadmap of USA: http://qist.lanl.gov/qcomp\_map.shtml - "Quantum communication with an accelerated partner", T. G. Downes, T. C. Ralph and N. Walk, Phys. Rev. A 87, 012327 (2013)
- "Black hole explosions?", Hawking, S. W., Nature 248 (5443): 30 (1974).
- "Experimental black hole evaporation”, Unruh, W.G., Phys. Rev. Lett., 46, 1351–1353, (1981).

Powered by

✕