The Thermodynamic Uncertainty Theorem
Kyle J. Ray,1, ∗Alexander B. Boyd,2, 3, 4, †Giacomo Guarnieri,5, ‡and James P. Crutchfield6, §
1Complexity Sciences Center and Physics Department,
University of California at Davis, One Shields Avenue, Davis, CA 95616, USA
2Corresponding author
3The Division of Physics, Mathematics and Astronomy,
California Institute of Technology, Pasadena, CA 91125, USA
4School of Physics, Trinity College Dublin, College Green, Dublin 2, D02 PN40, Ireland
5Dahlem Center for Complex Quantum Systems,
Freie Universit¨at Berlin, 14195 Berlin, Germany
6Complexity Sciences Center and Physics Department,
University of California at Davis, One Shields Avenue, Davis, CA 95616
Thermodynamic uncertainty relations (TURs) express a fundamental tradeoff between the preci-
sion (inverse scaled variance) of any thermodynamic current by functionals of the average entropy
production. Relying on purely variational arguments, we significantly extend these inequalities by
incorporating and analyzing the impact of higher statistical cumulants of entropy production within
a general framework of time-symmetrically controlled computation. This allows us to derive an ex-
act expression for the current that achieves the minimum scaled variance, for which the TUR bound
tightens to an equality that we name Thermodynamic Uncertainty Theorem (TUT). Importantly,
both the minimum scaled variance current and the TUT are functionals of the stochastic entropy
production, thus retaining the impact of its higher moments. In particular, our results show that,
beyond the average, the entropy production distribution’s higher moments have a significant effect
on any current’s precision. This is made explicit via a thorough numerical analysis of swap and
reset computations that quantitatively compares the TUT against previous generalized TURs. Our
results demonstrate how to interpolate between previously-established bounds and how to identify
the most relevant TUR bounds in different nonequilibrium regimes.
Keywords: thermodynamic uncertainty relation, entropy production, nonequilibrium steady state, current
Introduction. The past few decades witnessed sub-
stantial technological advances in miniaturization that,
today, have culminated in experimental realizations of
nanoscale thermal machines [1–8]. These devices ex-
hibit three fundamental features. First, they operate un-
der nonequilibrium conditions, i.e., either by keeping the
system in a nonequilibrium steady-state by means of volt-
age or temperature biases or through the application of
an external time-dependent control protocol. This im-
plies that a certain amount of entropy production Σ—
which quantifies the amount of irreversible dissipation
associated with nonequilibrium processes—is always gen-
erated [9]. Crucially, the entropy production limits heat
engine and refrigerator performance, constrains the phys-
ical mechanisms underlying complex biological function-
ing [10], and is the central quantity in Landauer’s infor-
mation erasure—the keystone of the bridge between ther-
modynamics and communication theory. Second, due to
their microscopic nature, the fluctuations of all thermo-
dynamic quantities (such as heat, work, and so on) be-
come as significant as their average values. Last, but
not least, the laws of quantum mechanics have impor-
tant repercussions for fluctuations, which generally have
both thermal and quantal origins [11–14].
Since Onsager’s and Kubo’s pioneering discovery of the
fluctuation-dissipation theorem (FDT) [15–17], deter-
mining the universal properties of fluctuations in out-
of-equilibrium processes, as well as their role in dissipa-
tion, has been a cornerstone of stochastic thermodynam-
ics. In the ‘90s, Jarzynski and Crooks generalized the
FDT through the fluctuation relations (FRs) [18–29]. At
the microscopic scale, the FRs refine the famous Second
Law of Thermodynamics hΣi ≥ 0 by determining the
full distribution of stochastic thermodynamic quantities
and thus their fluctuations. That is, the FRs replaced
the familiar Second law inequality with an equality from
which the Second Law is easily derived through Jensen’s
inequality.
More recently, a third milestone was crossed by con-
necting thermodynamic fluctuations out of equilibrium
to dissipation. These broad results, called thermo-
dynamic uncertainty relations (TURs), were originally
discovered in nonequilibrium steady-states of classical
time-homogeoneous Markov jump-processes satisfying lo-
cal detailed balance [30, 31]. Today, though, TURs
have been generalized to finite-time processes [32–34],
periodically-driven systems [35–41], Markovian quantum
systems undergoing Lindblad dynamics [42–44], and au-
tonomous classical [33, 45] and quantum [45–50] systems
in steady-states close to linear response.
arXiv:2210.00914v3 [cond-mat.stat-mech] 25 Nov 2022