52 research outputs found
Simplifying the design of multilevel thermal machines using virtual qubits
Quantum thermodynamics often deals with the dynamics of small quantum
machines interfacing with a large and complex environment. Virtual qubits,
collisional models and reset master equations have become highly useful tools
for predicting the qualitative behaviour of two-dimensional target systems
coupled to few-qubit machines and a thermal environment. While few successes in
matching the simplified model parameters for all possible physical systems are
known, the qualitative predictions still allow for a general design of quantum
machines irrespective of the implementation. We generalise these tools by
introducing multiple competing virtual qubits for modelling multi-dimensional
systems coupled to larger and more complex machines. By simulating the full
physical dynamics for targets with three dimensions, we uncover general
properties of reset models that can be used as `dials' to correctly predict the
qualitative features of physical changes in a realistic setup and thus design
autonomous quantum machines beyond a few qubits. We then present a general
analytic solution of the reset model for arbitrary-dimensional systems coupled
to multi-qubit machines. Finally, we showcase an improved three-level laser as
an exemplary application of our results.Comment: 9+6 pages, 6 figure
Quantum probe spectroscopy for cold atomic systems
We study a two-level impurity coupled locally to a quantum gas on an optical
lattice. For state-dependent interactions between the impurity and the gas, we
show that its evolution encodes information on the local excitation spectrum of
gas at the coupling site. Based on this, we design a nondestructive method to
probe the system's excitations in a broad range of energies by measuring the
state of the probe using standard atom optics methods. We illustrate our
findings with numerical simulations for quantum lattice systems, including
realistic dephasing noise on the quantum probe, and discuss practical limits on
the probe dephasing rate to fully resolve both regular and chaotic spectra.Comment: 17 single-column pages, 4 figures. Matches published versio
Bayesian parameter estimation using Gaussian states and measurements
Bayesian analysis is a framework for parameter estimation that applies even
in uncertainty regimes where the commonly used local (frequentist) analysis
based on the Cram\'er-Rao bound is not well defined. In particular, it applies
when no initial information about the parameter value is available, e.g., when
few measurements are performed. Here, we consider three paradigmatic estimation
schemes in continuous-variable quantum metrology (estimation of displacements,
phases, and squeezing strengths) and analyse them from the Bayesian
perspective. For each of these scenarios, we investigate the precision
achievable with single-mode Gaussian states under homodyne and heterodyne
detection. This allows us to identify Bayesian estimation strategies that
combine good performance with the potential for straightforward experimental
realization in terms of Gaussian states and measurements. Our results provide
practical solutions for reaching uncertainties where local estimation
techniques apply, thus bridging the gap to regimes where asymptotically optimal
strategies can be employed.Comment: 16+4 pages, 8 figure
Entanglement quantification in atomic ensembles
Entanglement measures quantify nonclassical correlations present in a quantum
system, but can be extremely difficult to calculate, even more so, when
information on its state is limited. Here, we consider broad families of
entanglement criteria that are based on variances of arbitrary operators and
analytically derive the lower bounds these criteria provide for two relevant
entanglement measures: the best separable approximation (BSA) and the
generalized robustness (GR). This yields a practical method for quantifying
entanglement in realistic experimental situations, in particular, when only few
measurements of simple observables are available. As a concrete application of
this method, we quantify bipartite and multipartite entanglement in
spin-squeezed Bose-Einstein condensates of atoms, by lower bounding
the BSA and the GR only from measurements of first and second moments of the
collective spin operator.Comment: Comments are welcom
Dynamical phase transitions and temporal orthogonality in one-dimensional hard-core bosons: from the continuum to the lattice
We investigate the dynamics of the rate function and of local observables after a quench in models which exhibit phase transitions between a superfluid and an insulator in their ground states. Zeros of the return probability, corresponding to singularities of the rate functions, have been suggested to indicate the emergence of dynamical criticality and we address the question of whether such zeros can be tied to the dynamics of physically relevant observables and hence order parameters in the systems. For this we first numerically analyze the dynamics of a hard-core boson gas in a one-dimensional waveguide when a quenched lattice potential is commensurate with the particle density. Such a system can undergo a pinning transition to an insulating state and we find non-analytic behavior in the evolution of the rate function which is indicative of dynamical phase transitions. In addition, we perform simulations of the time dependence of the momentum distribution and compare the periodicity of this collapse and revival cycle to that of the non-analyticities in the rate function: the two are found to be closely related only for deep quenches. We then confirm this observation by analytic calculations on a closely related discrete model of hard-core bosons in the presence of a staggered potential and find expressions for the rate function for the quenches. By extraction of the zeros of the survival amplitude we uncover a non-equilibrium timescale for the emergence of non-analyticities and discuss its relationship with the dynamics of the experimentally relevant parity operator
Endometrial Cancer Diagnosed at an Early Stage during Lynch Syndrome Surveillance: A Case Report
Lynch syndrome is an autosomal dominant inherited disorder caused by a germline pathogenic variant in DNA mismatch repair genes, resulting in multi-organ cancer. Annual transvaginal ultrasonography and endometrial biopsy are recommended for endometrial cancer surveillance in patients with Lynch syndrome in several guidelines; however, evidence is limited. Here, we present the case of a 51-year-old woman with endometrial cancer who underwent robot-assisted laparoscopic simple hysterectomy at an early stage detected by Lynch syndrome surveillance. The patient was a 51-year-old gravida zero woman without any medical history or symptoms. Her sister suffered from bladder, breast, rectal, and endometrial cancer and was diagnosed with Lynch syndrome using a hereditary cancer panel test (VistaSeq®). During gynecologic surveillance, the patient’s endometrial cytology was classified as Papanicolaou class III. Therefore, she underwent endometrial curettage with hysteroscopy and was diagnosed with atypical endometrial hyperplasia. Robot-assisted hysterectomy was performed with a final pathological diagnosis of endometrial cancer (endometrioid carcinoma, Grade 1), stage 1A. She has remained disease-free for more than 12 months. Owing to advances in genetic medicine, prophylactic and therapeutic surgeries for hereditary cancers are increasing. To achieve an early diagnosis and treatment of Lynch syndrome-associated cancers, the importance of Lynch syndrome surveillance should be more widely recognized
Microscopic contributions to the entropy production at all times: from nonequilibrium steady states to global thermalization
Based on exact integration of the Schrödinger equation, we numerically study microscopic contributions to the entropy production for the single electron transistor, a paradigmatic model describing a single Fermi level tunnel coupled to two baths of free fermions. To this end, we decompose the entropy production into a sum of information theoretic terms and study them across all relevant time scales, including the nonequilibrium steady state regime and the final stage of global thermalization. We find that the entropy production is dominated for most times by microscopic deviations from thermality in the baths and the correlation between (but not inside) the baths. Despite these microscopic deviations from thermality, the temperatures and chemical potentials of the baths thermalize as expected, even though our model is integrable. Importantly, this observation is confirmed for both initially mixed and pure states. We further observe that the bath-bath correlations are quite insensitive to the system-bath coupling strength contrary to intuition. Finally, the system-bath correlation, small in an absolute sense, dominates in a relative sense and displays pure quantum correlations for all studied parameter regimes
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