ORCID Profile
0000-0002-4247-3901
Current Organisation
University of Tokyo
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Publisher: American Physical Society (APS)
Date: 09-04-2019
Publisher: American Physical Society (APS)
Date: 10-05-2018
Publisher: American Physical Society (APS)
Date: 04-11-2020
Publisher: World Scientific Pub Co Pte Lt
Date: 07-01-2020
DOI: 10.1142/S0219749919410028
Abstract: Understanding temporal processes and their correlations in time is of paramount importance for the development of near-term technologies that operate under realistic conditions. Capturing the complete multi-time statistics that define a stochastic process lies at the heart of any proper treatment of memory effects. This is well understood in classical theory, where a hierarchy of joint probability distributions completely characterizes the process at hand. However, attempting to generalize this notion to quantum mechanics is problematic: observing realizations of a quantum process necessarily disturbs the state of the system, breaking an implicit, and crucial, assumption in the classical setting. This issue can be overcome by separating the experimental interventions from the underlying process, enabling an unambiguous description of the process itself and accounting for all possible multi-time correlations for any choice of interrogating instruments. In this paper, using a novel framework for the characterization of quantum stochastic processes, we first solve the long standing question of unambiguously describing the memory length of a quantum processes. This is achieved by constructing a quantum Markov order condition, which naturally generalizes its classical counterpart for the quantification of finite-length memory effects. As measurements are inherently invasive in quantum mechanics, one has no choice but to define Markov order with respect to the interrogating instruments that are used to probe the process at hand: different memory effects are exhibited depending on how one addresses the system, in contrast to the standard classical setting. We then fully characterize the structural constraints imposed on quantum processes with finite Markov order, shedding light on a variety of memory effects that can arise through various ex les. Finally, we introduce an instrument-specific notion of memory strength that allows for a meaningful quantification of the temporal correlations between the history and the future of a process for a given choice of experimental intervention. These findings are directly relevant to both characterizing and exploiting memory effects that persist for a finite duration. In particular, immediate applications range from developing efficient compression and recovery schemes for the description of quantum processes with memory to designing coherent control protocols that efficiently perform information-theoretic tasks, amongst a plethora of others.
Publisher: American Physical Society (APS)
Date: 09-04-2019
Publisher: Verein zur Forderung des Open Access Publizierens in den Quantenwissenschaften
Date: 27-04-2023
DOI: 10.22331/Q-2023-04-27-991
Abstract: In classical physics, memoryless dynamics and Markovian statistics are one and the same. This is not true for quantum dynamics, first and foremost because quantum measurements are invasive. Going beyond measurement invasiveness, here we derive a novel distinction between classical and quantum processes, namely the possibility of hidden quantum memory . While Markovian statistics of classical processes can always be reproduced by a memoryless dynamical model, our main result shows that this is not true in quantum mechanics: We first provide an ex le of quantum non-Markovianity whose manifestation depends on whether or not a previous measurement is performed – an impossible phenomenon for memoryless dynamics we then strengthen this result by demonstrating statistics that are Markovian independent of how they are probed, but are nonetheless s t i l l incompatible with memoryless quantum dynamics. Thus, we establish the existence of Markovian statistics gathered by probing a quantum process that nevertheless f u n d a m e n t a l l y require memory for their creation.
Publisher: American Physical Society (APS)
Date: 18-08-2022
Publisher: American Physical Society (APS)
Date: 10-12-2020
Publisher: American Physical Society (APS)
Date: 27-03-2023
Publisher: Springer Science and Business Media LLC
Date: 12-10-2021
DOI: 10.1038/S41534-021-00481-4
Abstract: Generic non-Markovian quantum processes have infinitely long memory, implying an exact description that grows exponentially in complexity with observation time. Here, we present a finite memory ansatz that approximates (or recovers) the true process with errors bounded by the strength of the non-Markovian memory. The introduced memory strength is an operational quantity and depends on the way the process is probed. Remarkably, the recovery error is bounded by the smallest memory strength over all possible probing methods. This allows for an unambiguous and efficient description of non-Markovian phenomena, enabling compression and recovery techniques pivotal to near-term technologies. We highlight the implications of our results by analyzing an exactly solvable model to show that memory truncation is possible even in a highly non-Markovian regime.
Publisher: American Physical Society (APS)
Date: 09-06-2021
No related grants have been discovered for Philip Taranto.