1. On Friday she will speak in our group meeting (11am, 6-310) about:
"Truly quantum Gibbs: Thermal state of a system whose charges don’t commute"
2. Tomorrow (Tues) she will speak at Harvard (1pm, Lyman 425)
"Go scramble yourself! Out-of-time-ordered correlators, fluctuation
relations, and quasiprobabilities"
She will give this talk again at UMass Boston on Tues May 30 (2pm, Science
Complex, Room ISC 1180).
3. A week from tomorrow (i.e. Tues May 23) she will speak at Harvard (11am,
Pfizer Lecture Hall in Harvard's Mallinckrodt building).
"MBL-mobile: Many-body-localized engine"
Abstracts are:
1.
During my last seminar at MIT, I asked you two questions about quantum
information and
thermodynamics: Consider a small system that exchanges heat and particles
with a bath. The
system thermalizes to the grand canonical ensemble. A quantum system may
exchange
conserved quantities, or “charges,” represented by operators that fail to
commute. Can such a
system thermalize? If so, what form does the thermal state have? These
questions concern truly
quantum thermodynamics. No one answered these questions when I asked you
them. I can’t
blame you: Deriving answers has taken three years. I’ll share what I’ve
learned.
References:
Yunger Halpern, P. Faist, J. Oppenheim, and A. Winter, Nat. Comms 7, 12051
(2016).
Yunger Halpern arXiv:1409.7845 (2014).
A. Martín Alhambra, M. Woods, and NYH (in prep).
2.
The out-of-time-ordered correlator (OTOC) reflects the scrambling of
quantum information in many-body systems. The OTOC encodes time reversals
and thermalization. So do fluctuation relations and quasiprobabilities.
Fluctuation relations are equalities derived in nonequilibrium statistical
mechanics. Quasiprobabilities are quantum generalizations of probabilities.
I will unite these three concepts in a fluctuation-type relation, casting
the OTOC as a moment of a summed quasiprobability. That
quasiprobability—and so the OTOC—can be inferred from weak measurements.
The weak-measurement scheme is expected to be implementable with
superconducting qubits, cold atoms, ion traps, cavity QED, and perhaps NMR.
This work offers conceptual and experimental insights into
quantum-information scrambling, fluctuation relations, and
quasiprobabilities.
References
(1) NYH, Phys. Rev. A 95, 012120 (2017).
(2) NYH, B. Swingle, and J. Dressel, arXiv:1704.01971 (2017).
3.
Many-body-localized (MBL) systems do not thermalize under their intrinsic
dynamics. This athermality, we propose, can be harnessed to perform
thermodynamic tasks. We illustrate by formulating an Otto engine cycle for
a quantum many-body system. The system is ramped between thermal and MBL
phases, if mesoscopic, or between weakly and strongly localized MBL
regimes, in the thermodynamic limit. MBL systems’ energy-level correlations
differ from thermal systems’. This discrepancy enhances the engine's
reliability, precludes worst-case trials, and enables mesoscale engines to
run in parallel in the thermodynamic limit. We estimate analytically and
calculate numerically the engine's efficiency and per-cycle power. The
efficiency mirrors the efficiency of the conventional thermodynamic Otto
cycle. The per-cycle power scales linearly with the system size and
inverse-exponentially with a localization length. This work introduces a
thermodynamic lens onto MBL, which, having been characterized recently, can
now be applied in thermodynamic tasks.
Reference: Coming soon!
Co-conspirators: Christopher D. White, Sarang Gopalakrishnan, Gil Refael
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