Research

(Last update: 2017)

My research interest is the foundation of statistical mechanics. In particular, my recent works are on

-Stochastic thermodynamics

-Thermalization in isolated quantum systems

Stochastic thermodynamics

-Power and efficiency of heat engines

Power and efficiency are two key quantities to characterize heat engines. To clarify general relation between efficiency and power has been a longstanding problem. Inspired by the method of partial entropy production (explained in the next part), I established a universal trade-off inequality between power and efficiency which holds as far as the engine is Markovian. This trade-off relation exhibits that an engine with higher efficiency has less power, and as its corollary we found a general no-go theorem that finite power engines never attain the Carnot efficiency, which has still been, maybe surprisingly, remained as an open problem.

In addition, employing the Lieb-Robinson bound, I proved another trade-off inequality between efficiency and the speed of operation for quantum non-Markovian heat engines. This relation again provides the aforementioned no-go theorem for non-Markovian engines.

N. Shiraishi, K. Saito, and H. Tasaki, Phys. Rev. Lett. 117, 190601 (2016).

N. Shiraishi and H. Tajima, arXiv preprint arXiv:1701.01914 (2017).

-Information thermodynamics

Thermodynamics under information processes with feedback control has been controversial topics since the proposal of Maxwell’s demon. Such a framework is called information thermodynamics, and it is considered to help our understanding of biological systems which show feedback control and sensing. In my researches, I clarified the stochastic role of information in thermodynamics with general information processes. In particular, I prove a fluctuation-theorem-type equality for general information processes.

To prove this, we propose the notion of partial entropy production, which is a decomposition of total entropy production and satisfies the integral fluctuation theorem individually. The partial entropy production opens the way to characterize thermodynamic properties of a single transition, not only a system or a subsystem.

N. Shiraishi and T. Sagawa, Phys. Rev. E 91, 012130 (2015).

N. Shiraishi, S. Ito, K. Kawaguchi, and T. Sagawa, New. J. Phys. 17, 045012 (2015).

N. Shiraishi, T. Matsumoto, and T. Sagawa, New J. Phys. 18, 013044 (2016).

S. Yamamoto, S. Ito, N. Shiraishi, and T. Sagawa, Phys. Rev. E 94, 052121 (2016).

-Autonomous engines

Autonomous (stationary) engines including Feynman’s ratchet, Brownian motors, and autonomous Maxwell’s demon are well studied in nonequilibrium statistical mechanics. In particular, I investigate the general condition for autonomous engines to attain the maximum (Carnot) efficiency. I establish the necessary and sufficient condition both in and beyond the linear response regime. This condition elucidates the significant difference between finite-size engines and macroscopic engines. These results clarify the tight-coupling condition beyond the linear response regime.

N. Shiraishi, Phys. Rev. E 92, 050101(R) (2015).

N. Shiraishi, Phys. Rev. E 95, 052128 (2017)

Thermalization in isolated quantum systems

How a pure quantum state thermalizes in an isolated quantum system is one of the most profound problem in statistical physics. To understand thermalization, the eigenstate thermalization hypothesis (ETH) is considered to be a key property, which claims that all energy eigenstates are thermal. It has been expected that (i) non-integrable non-localized systems satisfy the ETH, (ii) the ETH is a necessary condition for thermalization.

In contrast to such expectations, I introduce a systematic method to construct a Hamiltonian which is shift-invariant, short-range interaction, no local conserved quantities, but does not satisfy the ETH. The absence of ETH is proven analytically. In addition, numerical simulations show that a system with this Hamiltonian indeed thermalizes. This Hamiltonian is characterized by non-local conserved quantities, which induce a novel class of prethermalization phenomena.

N. Shiraishi and T. Mori, Phys. Rev. Lett. 119, 030601 (2017).

T. Mori and N. Shiraishi, arXiv preprint arXiv:1707.05921 (2017).