Cold-Atom Elevator: From Edge-State Injection to the Preparation of Fractional Chern Insulators.

Optical box traps offer new possibilities for quantum-gas experiments. Building on their exquisite spatial and temporal control, we propose to engineer system-reservoir configurations using box traps, in view of preparing and manipulating topological atomic states in optical lattices. First, we consider the injection of particles from the reservoir to the system: this scenario is shown to be particularly well suited to activating energy-selective chiral edge currents, but also to prepare fractional Chern insulating ground states. Then, we devise a practical evaporative-cooling scheme to effectively cool down atomic gases into topological ground states. Our open-system approach to optical-lattice settings provides a new path for the investigation of ultracold quantum matter, including strongly correlated and topological phases.

Indication of critical scaling in time during the relaxation of an open quantum system.

Near continuous phase transitions, universal power-law scaling, characterized by critical exponents, emerges. This behavior reflects the singular responses of physical systems to continuous control parameters like temperature or external fields. Universal scaling extends to non-equilibrium dynamics in isolated quantum systems after a quench, where time takes the role of the control parameter. Our research unveils critical scaling in time also during the relaxation dynamics of an open quantum system. Here we experimentally realize such a system by the spin of individual Cesium atoms dissipatively coupled through spin-exchange processes to a bath of ultracold Rubidium atoms. Through a finite-size scaling analysis of the entropy dynamics via numerical simulations, we identify a critical point in time in the thermodynamic limit. This critical point is accompanied by the divergence of a characteristic length, which is described by critical exponents that turn out to be unaffected by system specifics.

Quantum Trajectories for Time-Local Non-Lindblad Master Equations.

For the efficient simulation of open quantum systems, we often use quantum jump trajectories given by pure states that evolve stochastically to unravel the dynamics of the underlying master equation. In the Markovian regime, when the dynamics is described by a Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) master equation, this procedure is known as Monte Carlo wave function approach. However, beyond ultraweak system-bath coupling, the dynamics of the system is not described by an equation of GKSL type, but rather by the Redfield equation, which can be brought into pseudo-Lindblad form. Here, negative dissipation strengths prohibit the conventional approach. To overcome this problem, we propose a pseudo-Lindblad quantum trajectory (PLQT) unraveling. It does not require an effective extension of the state space, like other approaches, except for the addition of a single classical bit. We test the PLQT for the eternal non-Markovian master equation for a single qubit and an interacting Fermi-Hubbard chain coupled to a thermal bath and discuss its computational effort compared to solving the full master equation.

Cavity-Based Reservoir Engineering for Floquet-Engineered Superconducting Circuits.

Considering the example of superconducting circuits, we show how Floquet engineering can be combined with reservoir engineering for the controlled preparation of target states. Floquet engineering refers to the control of a quantum system by means of time-periodic forcing, typically in the high-frequency regime, so that the system is governed effectively by a time-independent Floquet Hamiltonian with novel interesting properties. Reservoir engineering, on the other hand, can be achieved in superconducting circuits by coupling a system of artificial atoms (or qubits) dispersively to pumped leaky cavities, so that the induced dissipation guides the system into a desired target state. It is not obvious that the two approaches can be combined, since reaching the dispersive regime, in which system and cavities exchange excitations only virtually, can be spoiled by driving-induced resonant transitions. However, working in the extended Floquet space and treating both system-cavity coupling as well as driving-induced excitation processes on the same footing perturbatively, we identify regimes, where reservoir engineering of targeted Floquet states is possible and accurately described by an effective time-independent master equation. We successfully benchmark our approach for the preparation of the ground state in a system of interacting bosons subjected to Floquet-engineered magnetic fields in different lattice geometries.

Facial Cutaneous Metastases of Gastric Signet-ring Cell Carcinoma: Resection and Reconstruction as a Palliative Surgical Treatment Option.

BACKGROUND: Cutaneous metastases of gastric signet-ring cell gastric carcinoma are very rare. Our following case report highlights the need for careful clinical examination and skin biopsy of newly developing scar-like or erythematous skin lesions in patients with a known history of malignant disease in order to prevent diagnostic and therapeutic delay. CASE REPORT: A 68-year-old male patient presented with two slightly painful, erythematous, facial skin lesions (chin and forehead) 2 years after gastrectomy for a signet-ring cell gastric carcinoma. The patient complained of intermittent neuropathic pain in the area of the mental nerve. A biopsy of both skin lesions demonstrated metastasis of signet-ring cell gastric carcinoma. Following discussion within the multidisciplinary tumor board, palliative surgical excision was recommended for this patient. Both skin lesions were resected and the large defect in the chin region was primarily closed by a cervical skin transposition flap. CONCLUSION: The presented case report of a patient with a known history of malignancy illustrates that newly developing erythematous skin lesions may be suspicious for cutaneous metastases. Palliative surgical interventions may play a role even in an advanced disease stage.

Lindbladian approximation beyond ultraweak coupling.

Away from equilibrium, the properties of open quantum systems depend on the details of their environment. A microscopic derivation of a master equation (ME) is therefore crucial. Of particular interest are Lindblad-type equations, not only because they provide the most general class of Markovian MEs, but also since they are the starting point for efficient quantum trajectory simulations. Lindblad-type MEs are commonly derived from the Born-Markov-Redfield equation via a rotating-wave approximation (RWA). However the RWA is valid only for ultraweak system-bath coupling and often fails to accurately describe nonequilibrium processes. Here we derive an alternative Lindbladian approximation to the Redfield equation, which does not rely on ultraweak system-bath coupling. Applying it to an extended Hubbard model coupled to Ohmic baths, we show that, especially away from equilibrium, it provides a good approximation in large parameter regimes where the RWA fails.

Design and characterization of a quantum heat pump in a driven quantum gas.

We propose the implementation of a quantum heat pump with ultracold atoms. It is based on two periodically driven coherently coupled quantum dots using ultracold atoms. Each dot possesses two relevant quantum states and is coupled to a fermionic reservoir. The working principle is based on energy-selective driving-induced resonant tunneling processes, where a particle that tunnels from one dot to the other either absorbs or emits the energy quantum ℏω associated with the driving frequency, depending on its energy. We characterize the device using Floquet theory and compare simple analytical estimates to numerical simulations based on the Floquet-Born-Markov formalism. In particular, we show that driving-induced heating is directly linked to the micromotion of the Floquet states of the system.

Phasonic Spectroscopy of a Quantum Gas in a Quasicrystalline Lattice.

Phasonic degrees of freedom are unique to quasiperiodic structures and play a central role in poorly understood properties of quasicrystals from excitation spectra to wave function statistics to electronic transport. However, phasons are challenging to access dynamically in the solid state due to their complex long-range character and the effects of disorder and strain. We report phasonic spectroscopy of a quantum gas in a one-dimensional quasicrystalline optical lattice. We observe that strong phasonic driving produces a nonperturbative high-harmonic plateau strikingly different from the effects of standard dipolar driving. Tuning the potential from crystalline to quasicrystalline, we identify spectroscopic signatures of quasiperiodicity and interactions and map the emergence of a multifractal energy spectrum, opening a path to direct imaging of the Hofstadter butterfly.

Bath-Induced Decay of Stark Many-Body Localization.

We investigate the relaxation dynamics of an interacting Stark-localized system coupled to a dephasing bath, and compare its behavior to the conventional disorder-induced many body localized system. Specifically, we study the dynamics of population imbalance between even and odd sites, and the growth of the von Neumann entropy. For a large potential gradient, the imbalance is found to decay on a timescale τ that grows quadratically with the Wannier-Stark tilt. For the noninteracting system, it shows an exponential decay, which becomes a stretched exponential decay in the presence of finite interactions. This is different from a system with disorder-induced localization, where the imbalance exhibits a stretched exponential decay also for vanishing interactions. As another clear qualitative difference, we do not find a logarithmically slow growth of the von Neumann entropy as it is found for the disordered system. Our findings can immediately be tested experimentally with ultracold atoms in optical lattices.

How to Directly Measure Floquet Topological Invariants in Optical Lattices.

The classification of topological Floquet systems with time-periodic Hamiltonians transcends that of static systems. For example, spinless fermions in periodically driven two-dimensional lattices are not completely characterized by the Chern numbers of the quasienergy bands, but rather by a set of winding numbers associated with the gaps. We propose a feasible scheme for measuring these winding numbers in a periodically driven optical lattice efficiently and directly. It is based on the construction of a one-parameter family of drives, continuously connecting the Floquet system of interest to a trivial reference system. The winding numbers are then determined by the identification and the tomography of the band-touching singularities occurring on the way. As a by-product, we also propose a method for probing spectral properties of time evolution operators via a time analog of crystallography.

Measuring topology from dynamics by obtaining the Chern number from a linking number.

Integer-valued topological indices, characterizing nonlocal properties of quantum states of matter, are known to directly predict robust physical properties of equilibrium systems. The Chern number, e.g., determines the quantized Hall conductivity of an insulator. Using non-interacting fermionic atoms in a periodically driven optical lattice, here we demonstrate experimentally that the Chern number determines also the far-from-equilibrium dynamics of a quantum system. Extending a respective proposal to Floquet systems, we measure the linking number that characterizes the trajectories of momentum-space vortices emerging after a strong quench. We observe that it directly corresponds to the ground-state Chern number. This one-to-one relation between a dynamical and a static topological index allows us to experimentally map out the phase diagram of our system. Furthermore, we measure the instantaneous Chern number and show that it remains zero under the unitary dynamics.

Floquet Engineering of Optical Solenoids and Quantized Charge Pumping along Tailored Paths in Two-Dimensional Chern Insulators.

The insertion of a local magnetic flux, as the one created by a thin solenoid, plays an important role in gedanken experiments of quantum Hall physics. By combining Floquet engineering of artificial magnetic fields with the ability of single-site addressing in quantum gas microscopes, we propose a scheme for the realization of such local solenoid-type magnetic fields in optical lattices. We show that it can be employed to manipulate and probe elementary excitations of a topological Chern insulator. This includes quantized adiabatic charge pumping along tailored paths inside the bulk, as well as the controlled population of edge modes.

On the number of Bose-selected modes in driven-dissipative ideal Bose gases.

In an ideal Bose gas that is driven into a steady state far from thermal equilibrium, a generalized form of Bose condensation can occur. Namely, the single-particle states unambiguously separate into two groups: the group of Bose-selected states, whose occupations increase linearly with the total particle number, and the group of all other states whose occupations saturate [Phys. Rev. Lett. 111, 240405 (2013)PRLTAO0031-900710.1103/PhysRevLett.111.240405]. However, so far very little is known about how the number of Bose-selected states depends on the properties of the system and its coupling to the environment. The answer to this question is crucial since systems hosting a single, a few, or an extensive number of Bose-selected states will show rather different behavior. While in the former two scenarios each selected mode acquires a macroscopic occupation, corresponding to (fragmented) Bose condensation, the latter case rather bears resemblance to a high-temperature state of matter. In this paper, we systematically investigate the number of Bose-selected states, considering different classes of the rate matrices that characterize the driven-dissipative ideal Bose gases in the limit of weak system-bath coupling. These include rate matrices with continuum limit, rate matrices of chaotic driven systems, random rate matrices, and rate matrices resulting from thermal baths that couple to a few observables only.

Current concepts in cleft care: A multicenter analysis.

The current surgical techniques used in cleft repair are well established, but different centers use different approaches. To determine the best treatment for patients, a multi-center comparative study is required. In this study, we surveyed all craniofacial departments registered with the German Society of Maxillofacial Surgery to determine which cleft repair techniques are currently in use. Our findings revealed much variation in cleft repair between different centers. Although most centers did use a two-stage approach, the operative techniques and timing of lip and palate closure were different in every center. This shows that a retrospective comparative analysis of patient outcome between the participating centers is not possible and illustrates the need for prospective comparative studies to establish the optimal technique for reconstructive cleft surgery.

Nasolabial Flap Improves Healing in Medication-Related Osteonecrosis of the Jaw.

PURPOSE: Medication-related osteonecrosis of the jaw (MRONJ) is an adverse side effect of antiresorptive and antiangiogenic therapeutic agents that is difficult to treat owing to its high relapse rate. The aim of the present study was to determine whether patients with MRONJ treated using decortication and a nasolabial flap compared with those who underwent decortication with mucoperiosteal flaps have better outcomes regarding stable wound closure. MATERIALS AND METHODS: Two groups of patients with MRONJ and intraoral exposed bone were evaluated in a cohort clinical study retrospectively. The primary predictor variable was the treatment group. The experimental group used the nasolabial flap for wound closure, and the control group used the mucoperiosteal flap for closure. The outcome variable was successful wound closure defined as a symptomless and closed wound after at least 12 months. Other study variables included factors such as perioperative drug holiday, duration of postoperative oral antibiotic administration, and postoperative use of nasogastric feeding tubes. Cox proportional hazard regression analysis and Kaplan-Meier curves were used to determine the factors independently associated with the dependent variable. The Mann-Whitney U test and χ2 test were used for analyses regarding group-related data. RESULTS: Both groups showed similar demographics. The 16 study patients receiving nasolabial flaps had a mean age of 69.9 years, and the 16 control patients receiving mucoperiosteal flaps had a mean age of 71.8 years. Both groups included 10 women and 6 men. Of the 16 patients in each group, 15 had received a bisphosphonate and 1, monoclonal antibody therapy. All evaluated patients underwent combined treatment, including decortication and intravenous antibiotics. Of the 16 patients receiving nasolabial flaps, symptomless intact wound closure was achieved in 68.8%. Of the 16 patients with mucoperiosteal closure, 18.7% achieved wound closure, with 81.2% developing a relapse of MRONJ, a statistically significant difference (P < .001). No statistically significant differences were found between the 2 groups in the demographic variables. The mean interval to relapse for the experimental and control groups was 13.6 ± 7.8 and 8.2 ± 7.9 months, respectively (P = .017). CONCLUSIONS: MRONJ is a complication of antiosteoclastic treatment of mostly oncologic, palliative patients, which requires a very methodical approach to surgical treatment. A variety of different methods have been reported. The use of nasolabial flaps can be considered as a highly reliable option for coverage the bone wound with less morbidity than microvascular free flaps and better long-term results compared with mucoperiosteal flaps.

Measuring the Single-Particle Density Matrix for Fermions and Hard-Core Bosons in an Optical Lattice.

Ultracold atoms in optical lattices provide clean, tunable, and well-isolated realizations of paradigmatic quantum lattice models. With the recent advent of quantum-gas microscopes, they now also offer the possibility to measure the occupations of individual lattice sites. What, however, has not yet been achieved is to measure those elements of the single-particle density matrix, which are off- diagonal in the occupation basis. Here, we propose a scheme to access these basic quantities both for fermions as well as hard-core bosons and investigate its accuracy and feasibility. The scheme relies on the engineering of a large effective tunnel coupling between distant lattice sites and a protocol that is based on measuring site occupations after two subsequent quenches.

Interaction Dependent Heating and Atom Loss in a Periodically Driven Optical Lattice.

Periodic driving of optical lattices has enabled the creation of novel band structures not realizable in static lattice systems, such as topological bands for neutral particles. However, especially driven systems of interacting bosonic particles often suffer from strong heating. We have systematically studied heating in an interacting Bose-Einstein condensate in a driven one-dimensional optical lattice. We find interaction dependent heating rates that depend on both the scattering length and the driving strength and identify the underlying resonant intra- and interband scattering processes. By comparing the experimental data and theory, we find that, for driving frequencies well above the trap depth, the heating rate is dramatically reduced by the fact that resonantly scattered atoms leave the trap before dissipating their energy into the system. This mechanism of Floquet evaporative cooling offers a powerful strategy to minimize heating in Floquet engineered quantum gases.

High-Temperature Nonequilibrium Bose Condensation Induced by a Hot Needle.

We investigate theoretically a one-dimensional ideal Bose gas that is driven into a steady state far from equilibrium via the coupling to two heat baths: a global bath of temperature T and a "hot needle," a bath of temperature T_{h}≫T with localized coupling to the system. Remarkably, this system features a crossover to finite-size Bose condensation at temperatures T that are orders of magnitude larger than the equilibrium condensation temperature. This counterintuitive effect is explained by a suppression of long-wavelength excitations resulting from the competition between both baths. Moreover, for sufficiently large needle temperatures ground-state condensation is superseded by condensation into an excited state, which is favored by its weaker coupling to the hot needle. Our results suggest a general strategy for the preparation of quantum degenerate nonequilibrium steady states with unconventional properties and at large temperatures.

Impact of Time Factors on Outcome in Patients with Head and Neck Cancer Treated with Definitive Radio(Chemo)Therapy.

AIM: To evaluate treatment-related factors such as overall treatment time (OTT) and radiation treatment time (RTT) in head-and-neck cancer. PATIENTS AND METHODS: A total of 216 patients with locoregionally advanced inoperable head and neck cancer were treated with definitive radio(chemo)therapy. Mean follow-up was 37 months. RESULTS: Median time from diagnosis to start of radiotherapy (total waiting time) was 34 days, and comprised of referral waiting time and time for preparatory work. Median RTT was 40 days, and median OTT was 91 days. At 6, 12 and 24 months local recurrence-free survival (LRFS) was 75%, 65% and 60%; metastasis-free survival (MFS) was 84%, 77% and 70%; overall survival (OS) was 72%, 58% and 40%. Tumor stage, boost and chemotherapy were significant for OS, waiting time for preparatory work and RTT were significant for MFS, and referral waiting time and total radiotherapy dose for LRFS. CONCLUSION: RTT ≤40 days was a prognostic factor for better MFS. Prolonged waiting time had a converse effect for radiotherapy with better outcome on MFS and LRFS.

Defining the surgical margins of adenoid cystic carcinoma and their impact on outcome: An international collaborative study.

BACKGROUND: The mainstay of treatment in adenoid cystic carcinoma (ACC) of the head and neck is surgical resection with negative margins. The purpose of this study was to define the margin status that associates with survival outcomes of ACC of the head and neck. METHODS: We conducted univariate and multivariate analyses of international data. RESULTS: Data of 507 patients with ACC of the head and neck were analyzed; negative margins defined as ≥5 mm were detected in 253 patients (50%). On multivariate analysis, the hazard ratios (HRs) of positive margin status were 2.68 (95% confidence interval [CI], 1.2-6.2; p = .04) and 2.63 (95% CI, 1.1-6.3; p = .03) for overall survival (OS) and disease-specific survival (DSS), respectively. Close margins had no significant impact on outcome, with HRs of 1.1 (95% CI, 0.4-3.0; p = .12) and 1.07 (95% CI, 0.3-3.4; p = .23) for OS and DSS, respectively, relative with negative margins. CONCLUSION: In head and neck ACC, positive margins are associated with the worst outcome. Negative or close margins are associated with improved outcome, regardless of the distance from the tumor. © 2017 Wiley Periodicals, Inc. Head Neck 39: 1008-1014, 2017.