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We consider quantum networks, where entangled photon pairs are distributed using fibre optic links from a centralized source to entangling nodes. The entanglement is then stored (via an entanglement swap) in entangling nodes' quantum memories until used in, e.g., distributed quantum computing, quantum key distribution, quantum sensing, and other applications. Due to the fibre loss, some photons are lost in transmission. Noise in the transmission link and the quantum memory also reduces fidelity. Thus, entangling nodes must keep updated records of photon-pair arrivals to each destination, and their use by the applications. This coordination requires classical information exchange between each entangled node pair. However, the same fibre link may not admit both classical and quantum transmissions, as the classical channels can generate enough noise (i.e., via spontaneous Raman scattering) to make the quantum link unusable. Here, we consider coordinating entanglement distribution using a standard Internet protocol (IP) network instead, and propose a control protocol to enable such. We analyse the increase in latency from transmission over an IP network, together with the effect of photon loss, quantum memory noise and buffer size, to determine the fidelity and rate of entangled pairs. We characterize the relationship between the latency of the non-ideal IP network and the decoherence time of the quantum memories, providing a comparison of promising quantum memory technologies.

Quantum computing platforms are subject to contradictory engineering requirements: qubits must be protected from mutual interactions when idling ('doing nothing'), and strongly interacting when in operation. If idling qubits are not sufficiently protected, information can 'leak' into neighbouring qubits, become non-locally distributed, and ultimately inaccessible. Candidate solutions to this dilemma include patterning-enhanced many-body localization, dynamical decoupling, and active error correction. However, no information-theoretic protocol exists to actually quantify this information loss due to internal dynamics in a similar way to e.g. SPAM errors or dephasing times. In this work, we develop a scalable, flexible, device non-specific protocol for quantifying this bitwise idle information loss based on the exploitation of tools from quantum information theory. We implement this protocol in over 3500 experiments carried out across 4 months (Dec 2023 - Mar 2024) on IBM's entire Falcon 5.11 series of processors. After accounting for other sources of error, and extrapolating results via a scaling analysis in shot count to zero shot noise, we detect idle information leakage to a high degree of statistical significance. This work thus provides a firm quantitative foundation from which the protection-operation dilemma can be investigated and ultimately resolved., Comment: 11 pages, 5 figures

We determine whether or not it is possible to identify many-body localization in quantum dot arrays, given their current technological capacities. We analyze the phase diagram of an extended Fermi-Hubbard model - a theoretical system that quantum dot arrays are known to simulate - using several quantities of varying experimental accessibility. By deriving the parameters of our model from our experimental system, we find that many-body localization can potentially be detected in current-generation quantum dot arrays. A pitfall that we identify is that the freezing of a system due to strong interactions yields signatures similar to conventional localization. We find that the most widely-used experimental signature of localization - the imbalance - is not sensitive to this fact, and may be unsuitable as the lone identifier of the many-body localized regime., Comment: 13 pages, 7 figures

A key feature of the many-body localized phase is the breaking of ergodicity and consequently the emergence of local memory; revealed as the local preservation of information over time. As memory is necessarily a time dependent concept, it has been partially captured by a few extant studies of dynamical quantities. However, these quantities are neither optimal, nor democratic with respect to input state; and as such a fundamental and complete information theoretic understanding of local memory in the context of many-body localization remains elusive. We introduce the dynamical Holevo quantity as the true quantifier of local memory, outlining its advantages over other quantities such as the imbalance or entanglement entropy. We find clear scaling behavior in its steady-state across the many-body localization transition, and determine a family of two-parameter scaling ans\"atze which captures this behavior. We perform a comprehensive finite size scaling analysis of this dynamical quantity extracting the transition point and scaling exponents., Comment: 8 pages, 4 figures, 1 table; added new section 2, other sections heavily revised, references added