Experimental Activation of Strong Local Passive States with Quantum Information
Nayeli A. Rodríguez-Briones · Hemant Katiyar · Eduardo Martín-Martínez · Raymond Laflamme
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In one page
Nayeli Rodríguez-Briones, Hemant Katiyar, Eduardo Martín-Martínez and Raymond Laflamme ran the experiment that quantum energy teleportation had been waiting for. Some quantum states are strong local passive: no operation you can perform on your own piece of the system, however clever, gets any energy out of it. Ground states are like that, and that is the technical reason nobody simply pumps the vacuum at a single spot. Masahiro Hotta had shown on paper that the block can be lifted when the state is entangled — measure the far end, send the answer down an ordinary classical channel, and the answer tells you which operation to apply at your end. The team ran that protocol on a nuclear magnetic resonance machine, using three carbon nuclei in a crotonic-acid molecule as the qubits, and measured energy coming out of the blocked end. The whole thing takes fourteen milliseconds, far faster than energy could cross the molecule, so nothing was smuggled through. The bookkeeping stays ordinary: the measurement pays.
Why it matters hereChapter 6 asks what it really takes to draw energy out of a ground state, and this is the first laboratory answer on an entangled system: the energy is already there as a suppressed local fluctuation, and a distant measurement result is the key that unlocks it. Chapter 2 gains a measured demonstration that a ground state carries structure its average energy does not show, and chapter 4 gains the connection the authors name themselves — the same protocol bears on violations of energy conditions in quantum field theory in curved spacetime, which is the exact quantity metric engineering asks for.
What it claims
01A state is strong local passive with respect to a Hamiltonian and a subsystem when energy cannot be extracted through any direct local quantum operation applied to that subsystem; the property holds for a wide range of states, from ground states to thermal states below a critical temperature and even strongly coupled heat baths in the thermodynamic limit.Introduction, paragraph 2; Figure 1(a)
Published and peer-reviewed02Adding local operations and classical communication breaks that block: a measurement on the distant subsystem A, the outcome sent to B down an ordinary classical channel, and an informed local unitary on B chosen by that outcome, together extract energy that was previously unavailable. If the outcome is not communicated to B, no energy can be extracted from B on average.Minimal QET model, Steps 1 to 3; the sentence following Equation 5
Published and peer-reviewed03Two conditions keep the accounting honest. Alice’s measurement operators must commute with the interacting term of the Hamiltonian, so that the energy her measurement injects does not raise the energy in Bob’s surroundings; and the protocol must be completed in a time shorter than the time energy would take to propagate from A to B.Minimal QET model, Step 1 and Step 2; the paragraph following Equation 6
Published and peer-reviewed04The experiment was run on a 700 megahertz nuclear magnetic resonance spectrometer using carbon-13-labelled trans-crotonic acid in acetone at an ambient 298 kelvin, with three carbon nuclei serving as the target B, an auxiliary system and the measured subsystem A. The two protocol unitaries took about ten and four milliseconds, a total of fourteen milliseconds, against a coupling time set by a spin-spin coupling of 1.16 hertz — far shorter than the time energy would need to cross from A to B.Experimental implementation; the paragraph beginning ‘The unitaries’
Published and peer-reviewed05Every experimental point gave energy extraction, beyond local and ambient noise and without energy transfer through the system: the first experimental activation of a strong local passive state, and the first confirmation that entanglement in a ground state allows local zero-point energy density to be activated.Experimental implementation, final paragraph; Conclusions, first paragraph; Figure 4
Published and peer-reviewed06The maximum possible amount of activated energy is reached only when the measurement device and the measured subsystem gain full mutual information and that outcome is transmitted to the target subsystem — and the protocol is proposed as a tool for local cooling of many-body systems, for the black-hole information problem, and for violations of energy conditions in quantum field theory in curved spacetimes.Conclusions, second and third paragraphs
What to watch
The way in
https://doi.org/10.1103/PhysRevLett.130.110801Published as Physical Review Letters, volume 130, article 110801, in the issue of 17 March 2023. The Crossref record carries the APS default licence and there is no Creative Commons statement in the text or on the arXiv record, so this page reproduces none of it. The claims below are read from the accepted manuscript, arXiv:2203.16269v2 of 14 April 2023, which is free to read at arxiv.org/abs/2203.16269 under the arXiv perpetual non-exclusive distribution licence; the printed paper runs eleven pages with seven figures and a supplemental material section. The authors are at the University of California Berkeley and the Miller Institute, the Institute for Quantum Computing and the Departments of Physics and Astronomy and of Applied Mathematics at the University of Waterloo, and the Perimeter Institute for Theoretical Physics. Masahiro Hotta’s introductory review of the protocol is on this site at /library/stm-5aa6b8b006 and Kazuki Ikeda’s superconducting-hardware demonstration at /library/stm-6f13e92d8b.
How to cite it
Nayeli A. Rodríguez-Briones, Hemant Katiyar, Eduardo Martín-Martínez, Raymond Laflamme (2023) Experimental Activation of Strong Local Passive States with Quantum Information. doi:10.1103/PhysRevLett.130.110801
Where it sits in the curriculum
Energy from the vacuumWhat the vacuum isThe unified pictureThe metric, warp drives and wormholes