Pseudomagic Quantum States.

Notions of nonstabilizerness, or "magic," quantify how nonclassical quantum states are in a precise sense: states exhibiting low nonstabilizerness preclude quantum advantage. We introduce "pseudomagic" ensembles of quantum states that, despite low nonstabilizerness, are computationally indistinguishable from those with high nonstabilizerness. Previously, such computational indistinguishability has been studied with respect to entanglement, introducing the concept of pseudoentanglement. However, we demonstrate that pseudomagic neither follows from pseudoentanglement nor implies it. In terms of applications, the study of pseudomagic offers fresh insights into the theory of quantum scrambling: it uncovers states that, even though they originate from nonscrambling unitaries, remain indistinguishable from scrambled states to any physical observer. Additional applications include new lower bounds on state synthesis problems, property testing protocols, and implications for quantum cryptography. Our Letter is driven by the observation that only quantities measurable by a computationally bounded observer-intrinsically limited by finite-time computational constraints-hold physical significance. Ultimately, our findings suggest that nonstabilizerness is a "hide-able" characteristic of quantum states: some states are much more magical than is apparent to a computationally bounded observer.

Unscrambling Quantum Information with Clifford Decoders.

Quantum information scrambling is a unitary process that destroys local correlations and spreads information throughout the system, effectively hiding it in nonlocal degrees of freedom. In principle, unscrambling this information is possible with perfect knowledge of the unitary dynamics [B. Yoshida and A. Kitaev, arXiv:1710.03363.]. However, this Letter demonstrates that even without previous knowledge of the internal dynamics, information can be efficiently decoded from an unknown scrambler by monitoring the outgoing information of a local subsystem. We show that rapidly mixing but not fully chaotic scramblers can be decoded using Clifford decoders. The essential properties of a scrambling unitary can be efficiently recovered, even if the process is exponentially complex. Specifically, we establish that a unitary operator composed of t non-Clifford gates admits a Clifford decoder up to t≤n.

Endoscopic vacuum therapy versus self-expandable metal stent for treatment of anastomotic leaks < 30 mm following oncologic Ivor-Lewis esophagectomy: a matched case-control study.

BACKGROUND: Management of anastomotic leaks after Ivor-Lewis esophagectomy remains a challenge. Although intracavitary endoscopic vacuum therapy (EVT) has shown great efficacy for large dehiscences, the optimal management of smaller leaks has not been standardized. This study aims to compare EVT versus self-expandable metal stent (SEMS) in the treatment of leaks < 30 mm in size, due to the lack of current data on this topic. METHODS: Patients undergoing EVT (cases) or SEMS (controls) between May 2017 and July 2022 for anastomotic leaks < 3 cm following oncologic Ivor-Lewis esophagectomy were enrolled. Controls were matched in a 1:1 ratio based on age (± 3 years), BMI (± 3 kg/m2) and leak size (± 4 mm). RESULTS: Cases (n = 22) and controls (n = 22) showed no difference in baseline characteristics and leak size, as per matching at enrollment. No differences were detected between the two groups in terms of time from surgery to endoscopic treatment (p = 0.11) or total number of procedures per patient (p = 0.05). Remarkably, the two groups showed comparable results in terms of leaks resolution (90.9% vs. 72.7%, p = 0.11). The number of procedures per patient was not significant between the two cohorts (p = 0.05). The most frequent complication in the SEMS group was migration (15.3% of procedures). CONCLUSION: EVT and SEMS seem to have similar efficacy outcomes in the treatment of anastomotic defects < 30 mm after Ivor-Lewis esophagectomy. However, larger studies are needed to corroborate these findings.

Stabilizer Rényi Entropy.

We introduce a novel measure for the quantum property of "nonstabilizerness"-commonly known as "magic"-by considering the Rényi entropy of the probability distribution associated to a pure quantum state given by the square of the expectation value of Pauli strings in that state. We show that this is a good measure of nonstabilizerness from the point of view of resource theory and show bounds with other known measures. The stabilizer Rényi entropy has the advantage of being easily computable because it does not need a minimization procedure. We present a protocol for an experimental measurement by randomized measurements. We show that the nonstabilizerness is intimately connected to out-of-time-order correlation functions and that maximal levels of nonstabilizerness are necessary for quantum chaos.

Isospectral Twirling and Quantum Chaos.

We show that the most important measures of quantum chaos, such as frame potentials, scrambling, Loschmidt echo and out-of-time-order correlators (OTOCs), can be described by the unified framework of the isospectral twirling, namely the Haar average of a k-fold unitary channel. We show that such measures can then always be cast in the form of an expectation value of the isospectral twirling. In literature, quantum chaos is investigated sometimes through the spectrum and some other times through the eigenvectors of the Hamiltonian generating the dynamics. We show that thanks to this technique, we can interpolate smoothly between integrable Hamiltonians and quantum chaotic Hamiltonians. The isospectral twirling of Hamiltonians with eigenvector stabilizer states does not possess chaotic features, unlike those Hamiltonians whose eigenvectors are taken from the Haar measure. As an example, OTOCs obtained with Clifford resources decay to higher values compared with universal resources. By doping Hamiltonians with non-Clifford resources, we show a crossover in the OTOC behavior between a class of integrable models and quantum chaos. Moreover, exploiting random matrix theory, we show that these measures of quantum chaos clearly distinguish the finite time behavior of probes to quantum chaos corresponding to chaotic spectra given by the Gaussian Unitary Ensemble (GUE) from the integrable spectra given by Poisson distribution and the Gaussian Diagonal Ensemble (GDE).

On-chip screening for prostate cancer: an EIS microfluidic platform for contemporary detection of free and total PSA.

Prostate cancer affects a large part of the western male population. The need for an early and accurate detection is thus a great challenge in common clinical practice, but the lack of specificity of the serum marker PSA (Prostate Specific Antigen) is a serious problem since its increased concentration can be related to several abnormalities. PSA, however, is found in serum in both a free and a complexed form with other proteins and the percentage amount of unbound PSA (the free-to-total PSA ratio) can be employed to distinguish prostate cancer from benign prostatic conditions, and also to predict the future risk of prostate cancer. To improve the operating characteristics of current PSA tests and to provide a clinical tool able to run label-free and sensitive analysis, we thus developed a biosensing platform based on Electrochemical Impedance Spectroscopy (EIS), which allows the contemporary detection of free and total PSA on a single biochip, enabling a quick screening for the risk of prostate cancer thanks to the presence of two different immobilized antibodies specific for the different antigens researched.