4 5 Massachusetts Institute of Technology. ( ) . The result follows by combining equations (1) and (2) and taking p=p(0), Pp=p(τ).
ORCID iDsJeremy A Owen https:/ /orcid.org/0000-0002-9180-3794 Artemy Kolchinsky https:/ /orcid.org/0000-0002-3518-9208
References[1] Shiraishi N, Funo K and Saito K 2018 Speed limit for classical stochastic processes Phys. Rev. Lett. 121 070601
AbstractWe consider the problem of how to construct a physical process over a finite state space X that applies some desired conditional distribution P to initial states to produce final states. This problem arises often in the thermodynamics of computation and nonequilibrium statistical physics more generally (e.g. when designing processes to implement some desired computation, feedback controller, or Maxwell demon). It was previously known that some conditional distributions cannot be implemented using any master equation that involves just the states in X. However, here we show that any conditional distribution P can in fact be implemented-if additional 'hidden' states not in X are available. Moreover, we show that it is always possible to implement P in a thermodynamically reversible manner. We then investigate a novel cost of the physical resources needed to implement a given distribution P: the minimal number of hidden states needed to do so. We calculate this cost exactly for the special case where P represents a single-valued function, and provide an upper bound for the general case, in terms of the non-negative rank of P. These results show that having access to one extra binary degree of freedom, thus doubling the total number of states, is sufficient to implement any P with a master equation in a thermodynamically reversible way, if there are no constraints on the allowed form of the master equation. (Such constraints can greatly increase the minimal needed number of hidden states.) Our results also imply that for certain P that can be implemented without hidden states, having hidden states permits an implementation that generates less heat.where p(0) and p(1) are column vectors whose entries sum to one, representing probability distributions at times t=0 and t=1 respectively. If our system has n states, the matrix P is an n×n stochastic matrix, representing the conditional distribution of the system state at the final time given its state at the initial time. The entry P ij is the probability that the system is in state i at the final time given that it was in state j at the initial time.