Squeezing Multilevel Atoms in Dark States via Cavity Superradiance

We describe a method to create and store scalable and long-lived entangled spin-squeezed states within a manifold of many-body cavity dark states using collective emission of light from multilevel atoms inside an optical cavity. We show that the system can be tuned to generate squeezing in a dark state where it will be immune to superradiance. We also show more generically that squeezing can be generated using a combination of superradiance and coherent driving in a bright state, and subsequently be transferred via single-particle rotations to a dark state where squeezing can be stored. Our findings, readily testable in current optical cavity experiments with alkaline-earth-like atoms, can open a path for dissipative generation and storage of metrologically useful states in optical transitions.

Quantum-enhanced greedy combinatorial optimization solver

Combinatorial optimization is a broadly attractive area for potential quantum advantage, but no quantum algorithm has yet made the leap. Noise in quantum hardware remains a challenge, and more sophisticated quantum-classical algorithms are required to bolster their performance. Here, we introduce an iterative quantum heuristic optimization algorithm to solve combinatorial optimization problems. The quantum algorithm reduces to a classical greedy algorithm in the presence of strong noise. We implement the quantum algorithm on a programmable superconducting quantum system using up to 72 qubits for solving paradigmatic Sherrington-Kirkpatrick Ising spin glass problems. We find the quantum algorithm systematically outperforms its classical greedy counterpart, signaling a quantum enhancement. Moreover, we observe an absolute performance comparable with a state-of-the-art semidefinite programming method. Classical simulations of the algorithm illustrate that a key challenge to reaching quantum advantage remains improving the quantum device characteristics.

Bosonic Pair Production and Squeezing for Optical Phase Measurements in Long-Lived Dipoles Coupled to a Cavity

We propose to simulate bosonic pair creation using large arrays of long-lived dipoles with multilevel internal structure coupled to an undriven optical cavity. Entanglement between the atoms, generated by the exchange of virtual photons through a common cavity mode, grows exponentially fast and is described by two-mode squeezing of effective bosonic quadratures. The mapping between an effective bosonic model and the natural spin description of the dipoles allows us to realize the analog of optical homodyne measurements via straightforward global rotations and population measurements of the electronic states, and we propose to exploit this for quantum-enhanced sensing of an optical phase (common and differential between two ensembles). We discuss a specific implementation based on Sr atoms and show that our sensing protocol is robust to sources of decoherence intrinsic to cavity platforms. Our proposal can open unique opportunities for next-generation optical atomic clocks.

Experimental Measurement of Out-of-Time-Ordered Correlators at Finite Temperature

Out-of-time-ordered correlators (OTOCs) are a key observable in a wide range of interconnected fields including many-body physics, quantum information science, and quantum gravity. Measuring OTOCs using near-term quantum simulators will extend our ability to explore fundamental aspects of these fields and the subtle connections between them. Here, we demonstrate an experimental method to measure OTOCs at finite temperatures and use the method to study their temperature dependence. These measurements are performed on a digital quantum computer running a simulation of the transverse field Ising model. Our flexible method, based on the creation of a thermofield double state, can be extended to other models and enables us to probe the OTOC's temperature-dependent decay rate. Measuring this decay rate opens up the possibility of testing the fundamental temperature-dependent bounds on quantum information scrambling.

Quantum Variational Learning of the Entanglement Hamiltonian

Learning the structure of the entanglement Hamiltonian (EH) is central to characterizing quantum many-body states in analog quantum simulation. We describe a protocol where spatial deformations of the many-body Hamiltonian, physically realized on the quantum device, serve as an efficient variational ansatz for a local EH. Optimal variational parameters are determined in a feedback loop, involving quench dynamics with the deformed Hamiltonian as a quantum processing step, and classical optimization. We simulate the protocol for the ground state of Fermi-Hubbard models in quasi-1D geometries, finding excellent agreement of the EH with Bisognano-Wichmann predictions. Subsequent on-device spectroscopy enables a direct measurement of the entanglement spectrum, which we illustrate for a Fermi Hubbard model in a topological phase.

Nonlinear Dynamics in a Synthetic Momentum-State Lattice

The scope of analog simulation in atomic, molecular, and optical systems has expanded greatly over the past decades. Recently, the idea of synthetic dimensions-in which transport occurs in a space spanned by internal or motional states coupled by field-driven transitions-has played a key role in this expansion. While approaches based on synthetic dimensions have led to rapid advances in single-particle Hamiltonian engineering, strong interaction effects have been conspicuously absent from most synthetic dimensions platforms. Here, in a lattice of coupled atomic momentum states, we show that atomic interactions result in large and qualitative changes to dynamics in the synthetic dimension. We explore how the interplay of nonlinear interactions and coherent tunneling enriches the dynamics of a one-band tight-binding model giving rise to macroscopic self-trapping and phase-driven Josephson dynamics with a nonsinusoidal current-phase relationship, which can be viewed as stemming from a nonlinear band structure arising from interactions.

Synthetic dimensions in ultracold polar molecules

Synthetic dimensions alter one of the most fundamental properties in nature, the dimension of space. They allow, for example, a real three-dimensional system to act as effectively four-dimensional. Driven by such possibilities, synthetic dimensions have been engineered in ongoing experiments with ultracold matter. We show that rotational states of ultracold molecules can be used as synthetic dimensions extending to many - potentially hundreds of - synthetic lattice sites. Microwaves coupling rotational states drive fully controllable synthetic inter-site tunnelings, enabling, for example, topological band structures. Interactions leads to even richer behavior: when molecules are frozen in a real space lattice with uniform synthetic tunnelings, dipole interactions cause the molecules to aggregate to a narrow strip in the synthetic direction beyond a critical interaction strength, resulting in a quantum string or a membrane, with an emergent condensate that lives on this string or membrane. All these phases can be detected using local measurements of rotational state populations.

Fermat's principle and the formal equivalence of local light-ray rotation and refraction at the interface between homogeneous media with a complex refractive index ratio

We derive a formal description of local light-ray rotation in terms of complex refractive indices. We show that Fermat's principle holds, and we derive an extended Snell's law. The change in the angle of a light ray with respect to the normal of a refractive index interface is described by the modulus of the refractive index ratio; the rotation around the interface normal is described by the argument of the refractive index ratio.

Helical CT angiography. A diagnostic problem solving technique

We describe a technique for making computed tomography (CT) angiographic studies more practical and workable. True CT angiography can be performed with arterial contrast injection combined with helical CT technique. Detailed angiographic images can be obtained; reconstructed images are aided by the helical technique, and other special studies can also be performed.

Adjuvant immunotherapy (BCG) in stage D prostate cancer

Thirty-three patients with advanced prostate cancer were prospectively randomized to receive either Bacillus Calmette-Guerin (BCG) adjuvant immunotherapy plus conventional therapy or conventional therapy alone. Conventional therapy consisted of estrogens or observation. There was a statistically significantly (p less than 0.05) longer survival in the 16 BCG-treated patients (42 weeks) than in the 17 control patients (29 weeks).

The immune response to prostate cancer: an evaluation and a review

The effects of stage and therapy of prostate cancer on the immune response were evaluated in 193 patients with an histologic diagnosis of prostatic malignancy. There was little or no effect, as measured by these generally non-specific tests, on the immune response. The host-tumor immune interaction is difficult to evaluate in prostate cancer. The complexities of measuring prostate tumor immunity are discussed and the literature is reviewed.

Urinary undiversion. Montreal Children's Hospital experience

Nine patients underwent urinary tract refunctionalization after prior supravesical diversion. Emphasis is placed on careful preoperative evaluation of these patients, including studies of renal and bladder function. In 8 patients continuity could be restored without interposition of bowel segment, while in the ninth case, this was necessary because of short ureteral lengths bilaterally. This was the only technical failure in this series requiring restoration of the diverted state. There was a dramatic improvement noted in the quality of life and mental status in the 8 patients in whom the procedure was successful.

The carcinoembryonic antigen test in urologic cancer

The diagnostic value of the CEA test was evaluated in 2,029 blood and urine samples from 308 patients with urologic cancer, 13 with nonurologic cancer, 20 urologic patients with nonmalignant disease, and in 30 controls. The blood CEA test was positive in 50% of the patients with active urologic cancer and in 35% of those with inactive cancer. The urine CEA test was elevated only in patients with active bladder cancer, but most of these had concurrently infected urines. At the present time, the CEA test does not reflect the accuracy necessary for an acceptable diagnostic test for the detection of urologic cancer.

Congential H-type tracheo-oesophageal fistula

Five cases of congenital H-type tracheo-oesophageal fistula are presented. The clinical features common to all were choking and coughing precipitated by feeds, recurrent chest infections, and episodes of abdominal distension. The usefulness of repeated oesophagograms in diagnosing the condition is emphasized. Operation in all cases was by the cervical approach. The single postoperative death was related to pre-existent severe chest infection, and no postoperative complications were encountered in the other patients.