An atomic boson sampler.

A boson sampler implements a restricted model of quantum computing. It is defined by the ability to sample from the distribution resulting from the interference of identical bosons propagating according to programmable, non-interacting dynamics1. An efficient exact classical simulation of boson sampling is not believed to exist, which has motivated ground-breaking boson sampling experiments in photonics with increasingly many photons2-12. However, it is difficult to generate and reliably evolve specific numbers of photons with low loss, and thus probabilistic techniques for postselection7 or marked changes to standard boson sampling10-12 are generally used. Here, we address the above challenges by implementing boson sampling using ultracold atoms13,14 in a two-dimensional, tunnel-coupled optical lattice. This demonstration is enabled by a previously unrealized combination of tools involving high-fidelity optical cooling and imaging of atoms in a lattice, as well as programmable control of those atoms using optical tweezers. When extended to interacting systems, our work demonstrates the core abilities required to directly assemble ground and excited states in simulations of various Hubbard models15,16.

Realizing spin squeezing with Rydberg interactions in an optical clock.

Neutral-atom arrays trapped in optical potentials are a powerful platform for studying quantum physics, combining precise single-particle control and detection with a range of tunable entangling interactions1-3. For example, these capabilities have been leveraged for state-of-the-art frequency metrology4,5 as well as microscopic studies of entangled many-particle states6-11. Here we combine these applications to realize spin squeezing-a widely studied operation for producing metrologically useful entanglement-in an optical atomic clock based on a programmable array of interacting optical qubits. In this demonstration of Rydberg-mediated squeezing with a neutral-atom optical clock, we generate states that have almost four decibels of metrological gain. In addition, we perform a synchronous frequency comparison between independent squeezed states and observe a fractional-frequency stability of 1.087(1) × 10-15 at one-second averaging time, which is 1.94(1) decibels below the standard quantum limit and reaches a fractional precision at the 10-17 level during a half-hour measurement. We further leverage the programmable control afforded by optical tweezer arrays to apply local phase shifts to explore spin squeezing in measurements that operate beyond the relative coherence time with the optical local oscillator. The realization of this spin-squeezing protocol in a programmable atom-array clock will enable a wide range of quantum-information-inspired techniques for optimal phase estimation and Heisenberg-limited optical atomic clocks12-16.

Half-minute-scale atomic coherence and high relative stability in a tweezer clock.

The preparation of large, low-entropy, highly coherent ensembles of identical quantum systems is fundamental for many studies in quantum metrology1, simulation2 and information3. However, the simultaneous realization of these properties remains a central challenge in quantum science across atomic and condensed-matter systems2,4-7. Here we leverage the favourable properties of tweezer-trapped alkaline-earth (strontium-88) atoms8-10, and introduce a hybrid approach to tailoring optical potentials that balances scalability, high-fidelity state preparation, site-resolved readout and preservation of atomic coherence. With this approach, we achieve trapping and optical-clock excited-state lifetimes exceeding 40 seconds in ensembles of approximately 150 atoms. This leads to half-minute-scale atomic coherence on an optical-clock transition, corresponding to quality factors well in excess of 1016. These coherence times and atom numbers reduce the effect of quantum projection noise to a level that is comparable with that of leading atomic systems, which use optical lattices to interrogate many thousands of atoms in parallel11,12. The result is a relative fractional frequency stability of 5.2(3) × 10-17τ-1/2 (where τ is the averaging time in seconds) for synchronous clock comparisons between sub-ensembles within the tweezer array. When further combined with the microscopic control and readout that are available in this system, these results pave the way towards long-lived engineered entanglement on an optical-clock transition13 in tailored atom arrays.

Microscopy of the interacting Harper-Hofstadter model in the two-body limit.

The interplay between magnetic fields and interacting particles can lead to exotic phases of matter that exhibit topological order and high degrees of spatial entanglement. Although these phases were discovered in a solid-state setting, recent innovations in systems of ultracold neutral atoms-uncharged atoms that do not naturally experience a Lorentz force-allow the synthesis of artificial magnetic, or gauge, fields. This experimental platform holds promise for exploring exotic physics in fractional quantum Hall systems, owing to the microscopic control and precision that is achievable in cold-atom systems. However, so far these experiments have mostly explored the regime of weak interactions, which precludes access to correlated many-body states. Here, through microscopic atomic control and detection, we demonstrate the controlled incorporation of strong interactions into a two-body system with a chiral band structure. We observe and explain the way in which interparticle interactions induce chirality in the propagation dynamics of particles in a ladder-like, real-space lattice governed by the interacting Harper-Hofstadter model, which describes lattice-confined, coherently mobile particles in the presence of a magnetic field. We use a bottom-up strategy to prepare interacting chiral quantum states, thus circumventing the challenges of a top-down approach that begins with a many-body system, the size of which can hinder the preparation of controlled states. Our experimental platform combines all of the necessary components for investigating highly entangled topological states, and our observations provide a benchmark for future experiments in the fractional quantum Hall regime.

High-risk ankle fractures in high-risk older patients: to fix or nail?

INTRODUCTION: Optimal treatment of high-risk ankle fractures in older, comorbid patients is unknown. Results of open reduction internal fixation (ORIF) versus tibiotalocalcaneal (TTC) fusion nailing for the treatment of high-risk geriatric ankle fractures were investigated. MATERIALS AND METHODS: Results of ORIF versus TTC fusion nailing were evaluated via retrospective case-control cohort study of 60 patients over age 50 with an open ankle fracture or one with at least 50% talar subluxation and at least 1 high-risk comorbidity: diabetes mellitus (DM), peripheral vascular disease, immunosuppression, active smoking, or a BMI > 35. The primary outcome was reoperation rate within 1-year post-surgery. Secondary outcomes include infection, peri-implant fracture, malunion/nonunion, mortality, length of stay, disposition, and hospital acquired complications. RESULTS: Mean age was 71 (ORIF) and 68 (TTC). 12/47 (25.5%) ORIF cases were open fractures versus 4/14 (28.6%) with TTC. There were no significant differences between ORIF and TTC in 1-year reoperation rates (17% vs 21.4%), infection rates (12.8% vs 14.3%), or union rates (76.% vs 85.7%), respectively. One TTC patient sustained a peri-implant fracture treated nonoperatively. There were no significant differences in medical risk factors between groups other than a higher rate of DM in the TTC group, 42.6% vs 78.6%, p = 0.02. Incomplete functional outcome data in this challenging patient cohort precluded drawing conclusions. CONCLUSION: ORIF and TTC fusion nailing result in comparable and acceptable reoperation, infection, and union rates in treating high-risk ankle fractures in patients over 50 with at least 1 major comorbidity for increased complications; further study is warranted.

Asymmetric Blockade and Multiqubit Gates via Dipole-Dipole Interactions.

Because of their strong and tunable interactions, Rydberg atoms can be used to realize fast two-qubit entangling gates. We propose a generalization of a generic two-qubit Rydberg-blockade gate to multiqubit Rydberg-blockade gates that involve both many control qubits and many target qubits simultaneously. This is achieved by using strong microwave fields to dress nearby Rydberg states, leading to asymmetric blockade in which control-target interactions are much stronger than control-control and target-target interactions. The implementation of these multiqubit gates can drastically simplify both quantum algorithms and state preparation. To illustrate this, we show that a 25-atom Greenberger-Horne-Zeilinger state can be created using only three gates with an error of 5.8%.

Nondestructive Cooling of an Atomic Quantum Register via State-Insensitive Rydberg Interactions.

We propose a protocol for sympathetically cooling neutral atoms without destroying the quantum information stored in their internal states. This is achieved by designing state-insensitive Rydberg interactions between the data-carrying atoms and cold auxiliary atoms. The resulting interactions give rise to an effective phonon coupling, which leads to the transfer of heat from the data atoms to the auxiliary atoms, where the latter can be cooled by conventional methods. This can be used to extend the lifetime of quantum storage based on neutral atoms and can have applications for long quantum computations. The protocol can also be modified to realize state-insensitive interactions between the data and the auxiliary atoms but tunable and nontrivial interactions among the data atoms, allowing one to simultaneously cool and simulate a quantum spin model.

Variational Spin-Squeezing Algorithms on Programmable Quantum Sensors.

Arrays of atoms trapped in optical tweezers combine features of programmable analog quantum simulators with atomic quantum sensors. Here we propose variational quantum algorithms, tailored for tweezer arrays as programmable quantum sensors, capable of generating entangled states on demand for precision metrology. The scheme is designed to generate metrological enhancement by optimizing it in a feedback loop on the quantum device itself, thus preparing the best entangled states given the available quantum resources. We apply our ideas to the generation of spin-squeezed states on Sr atom tweezer arrays, where finite-range interactions are generated through Rydberg dressing. The complexity of experimental variational optimization of our quantum circuits is expected to scale favorably with system size. We numerically show our approach to be robust to noise, and surpassing known protocols.

Measurement-Based Entanglement of Noninteracting Bosonic Atoms.

We demonstrate the ability to extract a spin-entangled state of two neutral atoms via postselection based on a measurement of their spatial configuration. Typically, entangled states of neutral atoms are engineered via atom-atom interactions. In contrast, in our Letter, we use Hong-Ou-Mandel interference to postselect a spin-singlet state after overlapping two atoms in distinct spin states on an effective beam splitter. We verify the presence of entanglement and determine a bound on the postselected fidelity of a spin-singlet state of (0.62±0.03). The experiment has direct analogy to creating polarization entanglement with single photons and hence demonstrates the potential to use protocols developed for photons to create complex quantum states with noninteracting atoms.

Rapid Production of Uniformly Filled Arrays of Neutral Atoms.

We demonstrate rapid loading of a small array of optical tweezers with a single ^{87}Rb atom per site. We find that loading efficiencies of up to 90% per tweezer are achievable in less than 170 ms for traps separated by more than 1.7 µm. Interestingly, we find the load efficiency is affected by nearby traps and present the efficiency as a function of the spacing between two optical tweezers. This enhanced loading, combined with subsequent rearranging of filled sites, will enable the study of quantum many-body systems via quantum gas assembly.

Contemporary management of open extremity fractures: What you need to know.

ABSTRACT: Open extremity fractures are high-risk injuries prone to significant complications, including soft tissue loss, bone defects, infection, infected nonunion, and the necessity for limb amputation. Large-scale multicenter prospective studies from the Lower Extremity Assessment Project and the Major Extremity Trauma Research Consortium have provided novel scientific insights pertinent to the timeliness and appropriateness of specific treatment modalities aimed at improving outcomes of patients with open extremity injuries. These include the imperative for early administration of intravenous antibiotics within 3 hours of injury, preferably within 1 hour of hospital admission. Unlike the proven value of early antibiotics, the time to initial surgical debridement does not appear to affect infection rates and patient outcomes. Recent evidence-based consensus guidelines from the American Academy of Orthopedic Surgeons provide scientific guidance for preventing surgical site infections in patients with open extremity fractures and support the decision making of limb salvage versus amputation in critical open extremity injuries. Patient survival represents the overarching priority in the management of any trauma patient with associated orthopedic injuries. Therefore, the timing and modality of managing open fractures must take into account the patient's physiology, response to resuscitation, and overall injury burden. The present review was designed to provide a state-of-the-art overview on the recommended diagnostic workup and management strategies for patients with open extremity fractures, based on the current scientific evidence.

Tweezer-programmable 2D quantum walks in a Hubbard-regime lattice.

Quantum walks provide a framework for designing quantum algorithms that is both intuitive and universal. To leverage the computational power of these walks, it is important to be able to programmably modify the graph a walker traverses while maintaining coherence. We do this by combining the fast, programmable control provided by optical tweezers with the scalable, homogeneous environment of an optical lattice. With these tools we study continuous-time quantum walks of single atoms on a square lattice and perform proof-of-principle demonstrations of spatial search with these walks. When scaled to more particles, the capabilities demonstrated can be extended to study a variety of problems in quantum information science, including performing more effective versions of spatial search using a larger graph with increased connectivity.

Vascular perfusion of a flexor carpi ulnaris muscle turnover pedicle flap for posterior elbow soft tissue reconstruction: a cadaveric study.

PURPOSE: The use of a pedicled flexor carpi ulnaris (FCU) muscle proximal turnover flap has been described previously for soft tissue reconstruction at the posterior elbow. Whereas consistent arterial supply to the FCU has been reported, the reliability of distal flap perfusion has not been confirmed. This study evaluated the vascular perfusion of an FCU turnover flap, based on the most proximal primary vascular pedicle that would permit a proximal turnover flap reconstruction to include the olecranon tip. METHODS: In 12 fresh-frozen, proximal humeral human amputation specimens, the FCU flap was elevated from distal to proximal, preserving the most proximal primary vascular pedicle to the muscle belly that would permit flap coverage of the olecranon tip. The axillary artery was injected with India ink after ligation of radial and ulnar arteries at the wrist. After injection, each specimen was sectioned transversely at 0.5-cm increments to assess vascular perfusion of the muscle using loupe magnification. RESULTS: The distance from the olecranon tip to the distal FCU muscle belly was 25.9 cm. The primary vascular pedicle that would facilitate creation of a proximal turnover flap was, on average, 5.9 cm distal to the olecranon tip. Perfusion of FCU muscle as measured distal to this primary pedicle was present in 50% to 100% of the muscle belly at an average of 8.9 cm beyond the pedicle. Perfusion of 25% to 50% of the FCU muscle belly was present at an average of 11.1 cm beyond the pedicle. Perfusion became less consistent (<25%) within the muscle belly at an average distance of 11.6 cm. CONCLUSIONS: Use of a proximally based, pedicled FCU muscle turnover flap provides a reliable option for soft tissue reconstruction at the posterior elbow. We observed consistent arterial perfusion of the muscle flap when preserving a proximal vascular pedicle 5.9 cm distal to the olecranon tip.

Citrobacter koseri as a cause of early periprosthetic infection after primary total hip arthroplasty.

Periprosthetic joint infection in the acute setting is usually caused by gram-positive species and remains a major problem facing total joint surgeons. We report a case of a 53-year-old male who presented with drainage 3 weeks after primary total hip arthroplasty. Citrobacter koseri was cultured from an infected hematoma in his deep tissues. Surgical treatment included irrigation and debridement with femoral head and liner exchange. He received a 6-week course of ertapenem and is currently asymptomatic. We present C. koseri as a rare cause of acute periprosthetic infection and offer an effective treatment protocol.

Photons and qubits get a better connection.

Quantum networks will require versatile quantum interconnects.

High-power, fiber-laser-based source for magic-wavelength trapping in neutral-atom optical clocks.

We present a continuous-wave, 810 nm laser with watt-level powers. Our system is based on difference-frequency generation of 532 and 1550 nm fiber lasers in a single pass through periodically poled lithium niobate. We measure the broadband spectral noise and relative intensity noise to be compatible with off-resonant dipole trapping of ultracold atoms. Given the large bandwidth of the fiber amplifiers, the output can be optimized for a range of wavelengths, including the strontium clock-magic-wavelength of 813 nm. Furthermore, with the exploration of more appropriate nonlinear crystals, we believe that there is a path toward scaling this proof-of-principle design to many watts of power and that this approach could provide a robust, rack-mountable trapping laser for future use in strontium-based optical clocks.

Fracture of highly cross-linked all-polyethylene patella after total knee arthroplasty.

Recent advances in polyethylene fabrication have led to the introduction of highly cross-linked polyethylene tibial and patellar components for use in total knee arthroplasty (TKA) with the goal of reducing wear-related osteolysis. However, some reports suggest decreased mechanical strength as a result of the additional thermal and sterilization treatments in the manufacturing of implants. Complications related to the patella are among the most common causes of failure in TKA, but patellar component fracture is rare. The authors report a case of a highly cross-linked all-polyethylene patellar component that failed as a result of fracture in vivo in a patient 3 years after TKA.

Timing of Treatment of Open Fractures of the Distal Radius in Patients Younger Than 65 Years.

The authors aimed to characterize surgical and functional outcomes of open fractures of the distal radius in patients younger than 65 years. At their level I trauma center, the authors conducted a retrospective review of 92 patients (age range, 16-64 years) who had 94 open fractures of the distal radius (average follow-up, 30 months; range, 3-95 months). Sixty-four fractures received definitive treatment at the time of initial débridement; 30 received definitive fixation and soft tissue coverage after staged débridement. Primary surgical outcome was development of deep surgical site infection requiring repeat surgical débridement; secondary surgical outcome was surgical complications requiring reoperation. Functional outcome was assessed by wrist range of motion. Overall infection rate was 15% (14 of 94 fractures). Seven (11%) of 64 fractures in the immediate definitive fixation group developed infection compared with 7 (23%) of 30 fractures in the staged treatment group (P=.13). Twenty-one (33%) of 64 fractures in the immediate definitive fixation group required reoperation compared with 15 (50%) of 30 in the staged treatment group (P=.11). Deep surgical site infections and surgical complications associated with open fractures of the distal radius are driven by soft tissue injury. [Orthopedics. 2019; 42(4):219-225.].

Probing entanglement in a many-body-localized system.

An interacting quantum system that is subject to disorder may cease to thermalize owing to localization of its constituents, thereby marking the breakdown of thermodynamics. The key to understanding this phenomenon lies in the system's entanglement, which is experimentally challenging to measure. We realize such a many-body-localized system in a disordered Bose-Hubbard chain and characterize its entanglement properties through particle fluctuations and correlations. We observe that the particles become localized, suppressing transport and preventing the thermalization of subsystems. Notably, we measure the development of nonlocal correlations, whose evolution is consistent with a logarithmic growth of entanglement entropy, the hallmark of many-body localization. Our work experimentally establishes many-body localization as a qualitatively distinct phenomenon from localization in noninteracting, disordered systems.

Seconds-scale coherence on an optical clock transition in a tweezer array.

Coherent control of high-quality factor optical transitions in atoms has revolutionized precision frequency metrology. Leading optical atomic clocks rely on the interrogation of such transitions in either single ions or ensembles of neutral atoms to stabilize a laser frequency at high precision and accuracy. We demonstrate a platform that combines the key strengths of these two approaches, based on arrays of individual strontium atoms held within optical tweezers. We report coherence times of 3.4 seconds, single-ensemble duty cycles up to 96% through repeated interrogation, and frequency stability of 4.7 × 10-16 (τ/s)-1/2 These results establish optical tweezer arrays as a powerful tool for coherent control of optical transitions for metrology and quantum information science.