STM-D-0450Paper2023Published and peer-reviewed

Demonstration of Quantum Energy Teleportation on Superconducting Quantum Hardware

Kazuki Ikeda

Abstract and summary · read the original at the source

In one page

Kazuki Ikeda, at Stony Brook University, ran a protocol on IBM’s public quantum computers that moves energy — not a description of energy, but a usable amount of it — using nothing but a phone call. Quantum energy teleportation, proposed by Masahiro Hotta about fifteen years earlier, works like this. Two qubits sit in the entangled ground state of a small system. Alice measures her qubit; the measuring device injects energy, and the local entanglement is broken. She then sends Bob one classical bit, heads or tails. Because the ground state’s correlations already reach across to Bob, that single bit tells him exactly which operation to perform on his own qubit, and performing it lets his device draw energy back out of the system. Ikeda built the two-qubit circuit for it, six gates deep, ran it on six IBM machines including one free to anyone in the world, and measured the local energy going below the ground-state level exactly as the theory says.

Why it matters hereChapter 6 is about drawing usable energy out of the structure of the vacuum, and this is the cleanest laboratory version of the idea: the energy comes from correlations already present in the ground state, released by a local operation that only a distant measurement result can specify. Chapter 2 gains a working demonstration that a ground state has more structure than its average energy suggests. The bookkeeping stays ordinary throughout — Alice’s device puts the energy in and Bob’s device takes it out — which is exactly why the result is checkable. Hotta’s review of the protocol is on this site at /library/stm-5aa6b8b006 and the distance-free version at /library/stm-2e579e12bc.

What it claims

01Quantum energy teleportation, proposed by Hotta about fifteen years before this paper and since studied for spin chains, an ion-trap system and a quantum Hall system, transfers energy using only local operations and classical communication: it is classical information rather than energy that travels the channel, and the intermediate subsystem between sender and receiver is not excited by the system’s energy carriers during the short duration of the protocol. It had been experimentally validated once before, in a nuclear magnetic resonance setup.Section I, opening paragraphs, citing references 5 to 12 and 20
Published and peer-reviewed
02The energy bookkeeping is ordinary and stated explicitly: any non-trivial local operation on the ground state of a many-body system raises its energy, and that increase is supplied by the measuring device. Because the pre-existing entanglement stores information about the injected energy at locations away from Alice, operations near Alice alone cannot recover it; Bob’s conditional operation, chosen using her result, is what allows his device to extract energy from the system, with conservation of energy holding throughout.Section I, third and fourth paragraphs; Equations 6 and 13
Settled physics
03The minimal model runs on two qubits with a maximum circuit depth of six. The exact ground state is prepared with one rotation and one CNOT; the constants in the Hamiltonian are chosen so that this ground state reads zero energy for every local and global piece of it; Alice’s projective measurement of her Pauli X operator deposits a mean energy of h squared divided by the square root of h squared plus k squared; and Bob applies a rotation whose angle is fixed by h and k. Since the coupling term always has a negative expectation value and Bob’s local term always a positive one, it is enough for Bob to measure the coupling term alone to receive energy.Section II, subsections A to C, Equations 7 to 14; Figure 1
Published and peer-reviewed
04The central measurement is the observation of a local energy below the level the ground state defines as zero. Ikeda reports a negative coupling-term expectation value for every combination of the two model parameters on every machine used — six IBM devices, ibmq lima, ibmq jakarta, ibmq hanoi, ibm cairo, ibm auckland and ibmq montreal — with the closest approach to the exact value being minus 0.1079 at h of 1.5 and k of 1 on ibmq jakarta, about 76 percent of the analytic result. A simple measurement-error mitigation built from four calibration circuits improved the raw hardware values, in some cases enough to bring the negative expectation value into view.Section II D, Table I and Figure 2(B); Tables III and IV in the appendices
Published and peer-reviewed
05The transfer beats the system’s own dynamics. Alice must report her result within a time far shorter than the coupling timescale, and in this experiment that meant of order ten nanoseconds against a coupling time of order one hundred; on the hardware a single-qubit operation takes 20 to 40 nanoseconds while a two-qubit CNOT takes 200 to 500, so Bob extracts his energy faster than the natural unitary evolution of the system could carry energy from Alice to him.Section I, fifth paragraph; Section II D and Table III
Published and peer-reviewed
06The protocol is now a reproducible benchmark rather than a proposal: a two-qubit device six gates deep is enough, the circuits are published as open-access code, and the machine properties are public in real time, so anyone can repeat the run. The named next steps are a version with no limit of distance and a universal protocol for arbitrarily large quantum networks, with the milestone being quantum energy teleportation across a real network — the author points to the 158 kilometre Stony Brook to Brookhaven link on Long Island, and to quantum networks expected in practical use around the 2030s.Section I, second paragraph; Section III, first two paragraphs, citing references 21, 26 and 27
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Read it · abstract

Abstract

Teleporting physical quantities to remote locations is a remaining key challenge for quantum information science and technology. Quantum teleportation has enabled the transfer of quantum information, but teleportation of quantum physical quantities has not yet been realized. Here we report the realization and observation of quantum energy teleportation on real superconducting quantum hardware. We achieve this by using several IBM's superconducting quantum computers. The results are consistent with the exact solution of the theory and are improved by the mitigation of measurement error. Quantum energy teleportation requires only local operations and classical communication. Therefore our results provide a realistic benchmark that is fully achievable with current quantum computing and communication technologies.

Kazuki Ikeda, Co-design Center for Quantum Advantage and Center for Nuclear Theory, Department of Physics and Astronomy, Stony Brook University. Published as Physical Review Applied 20, 024051 (2023); preprint arXiv:2301.02666v5.

(Abstract only — see the rights note above for why the full text is not reproduced here. The complete paper, with the minimal-model Hamiltonian, the ground-state preparation circuit, Alice’s deposit step and Bob’s conditional operation, the deferred-measurement trick for hardware without mid-circuit conditionals, the six machine layouts, the measured and error-mitigated expectation values and the appendices on machine properties, is at the source. Hotta’s introductory review of the protocol is on this site at /library/stm-5aa6b8b006, and the version without a limit of distance at /library/stm-2e579e12bc.)

The way in

https://doi.org/10.1103/PhysRevApplied.20.024051LICENCE. Published as Physical Review Applied 20, 024051 (21 August 2023); the Crossref record carries the APS default licence and the APS default accepted-manuscript licence, and the preprint, arXiv:2301.02666v5 of 22 August 2023, carries the arXiv.org perpetual non-exclusive distribution licence. No Creative Commons statement appears in the text or on the arXiv record, so this page holds the summary, the claims and the author’s own abstract and sends the reader to the source. The claims below are read from the preprint text. The quantum circuits themselves are published by the author as open-access code. Hotta’s introductory review of the protocol is on this site at /library/stm-5aa6b8b006 and the distance-free version at /library/stm-2e579e12bc.

How to cite it

Kazuki Ikeda (2023) Demonstration of Quantum Energy Teleportation on Superconducting Quantum Hardware. doi:10.1103/PhysRevApplied.20.024051

Where it sits in the curriculum

The evidence ladder What the vacuum is Energy from the vacuum