Quantum Nonlinear Optics Based on Two-Dimensional Rydberg Atom Arrays.

We propose the combination of subwavelength, two-dimensional atomic arrays and Rydberg interactions as a powerful platform to realize strong, coherent interactions between individual photons with high fidelity. The atomic spatial ordering guarantees efficient atom-light interactions without the possibility of scattering light into unwanted directions, allowing the array to act as a perfect mirror for individual photons. In turn, Rydberg interactions enable single photons to alter the optical response of the array within a potentially large blockade radius R_{b}, which can effectively punch a large "hole" for subsequent photons. We show that such a system enables a coherent photon-photon gate or switch, with a significantly better error scaling (∼R_{b}^{-4}) than in a disordered ensemble. We also investigate the optical properties of the system in the limit of strong input intensities and show that this many-body quantum driven dissipative system can be modeled well by a semiclassical model based on holes punched in a classical mirror.

Topological Quantum Optics Using Atomlike Emitter Arrays Coupled to Photonic Crystals.

We propose an experimentally feasible nanophotonic platform for exploring many-body physics in topological quantum optics. Our system is composed of a two-dimensional lattice of nonlinear quantum emitters with optical transitions embedded in a photonic crystal slab. The emitters interact through the guided modes of the photonic crystal, and a uniform magnetic field gives rise to large topological band gaps, robust edge states, and a nearly flat band with a nonzero Chern number. The presence of a topologically nontrivial nearly flat band paves the way for the realization of fractional quantum Hall states and fractional topological insulators in a topological quantum optical setting.

[Expression of anaplastic lymphoma kinase clone 1A4 in pediatric medulloblastoma and its significance].

Objective: To investigate the immunohistochemical staining of anaplastic lymphoma kinase (ALK; clone 1A4) in pediatric medulloblastoma (MB). Methods: Molecular subtyping was performed based on the NanoString and sequencing techniques for 44 pediatric MB cases at Children's Hospital, Zhejiang University School of Medicine from 2014 to 2017. ALK expression was detected with EnVision immunhistochemistry using ALK clone 1A4 on whole section. Statistical analyses were performed to evaluate the correlation of protein expression with molecular subgroups. Results: The age ranged from 0.5 to 13.0 years with an average age of 5.8 years. There were 28 males and 16 females, and 31 classic, 5 desmoplastic nodular, 3 extensive nodular and 5 large cell/anaplastic MBs. Except three cases was unable classified, 41 MBs were classified into the four molecular groups: 5 in WNT group, 12 in SHH group, 9 in Group 3 and 15 in Group 4. Thirteen of 44 MB cases were positive staining for ALK, and the positive rate was 29.5%. Six cases were strong reaction, and 7 cases were weak. The expression of ALK at the protein level was associated with the WNT group (P<0.01). The characteristic perinuclear dot-like staining was only showed in WNT group. Conclusions: The ALK immunhistochemistry using antibody clone 1A4 is a useful marker for the molecular subgroup detection of MB. The strong staining and perinuclear dot-like staining indicate as WNT group.

[Application of the pathological classification of "CCCG-WT-2016" (2019 revision) for treatment of Wilms tumors].

Objective: To describe our experiences in application of the 2019 revision of "CCCG-WT-2016" for the diagnosis of Wilms tumors. Methods: Ninety-one cases of Wilms tumor diagnosed at Shanghai Children's Medical Center from January 2015 to December 2018 were collected. All cases were reviewed by two senior pathologists, including one from China and the other from Singapore, according to the 2019 revision of "CCCG-WT-2016." Results: The specimens were obtained by core biopsy (n=21), primary nephrectomy (n=41), post-chemotherapy nephrectomy/resection (n=18), or biopsy/resection of metastatic/relapse/post-chemotherapy metastatic lesion(s) (n=11). The specimens of core biopsy and primary nephrectomy (n=62) all had favorable histology.Twelve post-chemotherapy nephrectomy cases were subdivided into three risk groups: low risk (n=0), intermediate risk (n=10) and high risk (n=2). Six post-chemotherapy resection cases were subdivided into 3 risk groups:low risk (n=0), intermediate risk (n=5) and high risk (n=1). The remaining 11 cases were comprised of metastatic, relapse, and post-chemotherapy metastatic lesions. The concordance rate of the two senior pathologists was 100%(91/91). Conclusions: The 2019 revision of "CCCG-WT-2016" is clearly written and easy to use. It can serve as the basis of accurate classification for clinical treatment.

Optimization of photon storage fidelity in ordered atomic arrays.

A major application for atomic ensembles consists of a quantum memory for light, in which an optical state can be reversibly converted to a collective atomic excitation on demand. There exists a well-known fundamental bound on the storage error, when the ensemble is describable by a continuous medium governed by the Maxwell-Bloch equations. However, these equations are semi-phenomenological, as they treat emission of the atoms into other directions other than the mode of interest as being independent. On the other hand, in systems such as dense, ordered atomic arrays, atoms interact with each other strongly and spatial interference of the emitted light might be exploited to suppress emission into unwanted directions, thereby enabling improved error bounds. Here, we develop a general formalism that fully accounts for spatial interference, and which finds the maximum storage efficiency for a single photon with known spatial input mode into a collection of atoms with discrete, known positions. As an example, we apply this technique to study a finite two-dimensional square array of atoms. We show that such a system enables a storage error that scales with atom number N a like ∼ ( log N a ) 2 ∕ N a 2 , and that, remarkably, an array of just 4 × 4 atoms in principle allows for an error of less than 1%, which is comparable to a disordered ensemble with an optical depth of around 600.

Topological Quantum Optics in Two-Dimensional Atomic Arrays.

We demonstrate that two-dimensional atomic emitter arrays with subwavelength spacing constitute topologically protected quantum optical systems where the photon propagation is robust against large imperfections while losses associated with free space emission are strongly suppressed. Breaking time-reversal symmetry with a magnetic field results in gapped photonic bands with nontrivial Chern numbers and topologically protected, long-lived edge states. Due to the inherent nonlinearity of constituent emitters, such systems provide a platform for exploring quantum optical analogs of interacting topological systems.

Electromagnetically induced transparency and slow light with optomechanics.

Controlling the interaction between localized optical and mechanical excitations has recently become possible following advances in micro- and nanofabrication techniques. So far, most experimental studies of optomechanics have focused on measurement and control of the mechanical subsystem through its interaction with optics, and have led to the experimental demonstration of dynamical back-action cooling and optical rigidity of the mechanical system. Conversely, the optical response of these systems is also modified in the presence of mechanical interactions, leading to effects such as electromagnetically induced transparency (EIT) and parametric normal-mode splitting. In atomic systems, studies of slow and stopped light (applicable to modern optical networks and future quantum networks) have thrust EIT to the forefront of experimental study during the past two decades. Here we demonstrate EIT and tunable optical delays in a nanoscale optomechanical crystal, using the optomechanical nonlinearity to control the velocity of light by way of engineered photon-phonon interactions. Our device is fabricated by simply etching holes into a thin film of silicon. At low temperature (8.7 kelvin), we report an optically tunable delay of 50 nanoseconds with near-unity optical transparency, and superluminal light with a 1.4 microsecond signal advance. These results, while indicating significant progress towards an integrated quantum optomechanical memory, are also relevant to classical signal processing applications. Measurements at room temperature in the analogous regime of electromagnetically induced absorption show the utility of these chip-scale optomechanical systems for optical buffering, amplification, and filtering of microwave-over-optical signals.

Deterministic Generation of Arbitrary Photonic States Assisted by Dissipation.

A scheme to utilize atomlike emitters coupled to nanophotonic waveguides is proposed for the generation of many-body entangled states and for the reversible mapping of these states of matter to photonic states of an optical pulse in the waveguide. Our protocol makes use of decoherence-free subspaces (DFSs) for the atomic emitters with coherent evolution within the DFSs enforced by strong dissipative coupling to the waveguide. By switching from subradiant to superradiant states, entangled atomic states are mapped to photonic states with high fidelity. An implementation using ultracold atoms coupled to a photonic crystal waveguide is discussed.

Coupling graphene mechanical resonators to superconducting microwave cavities.

Graphene is an attractive material for nanomechanical devices because it allows for exceptional properties, such as high frequencies, quality factors, and low mass. An outstanding challenge, however, has been to obtain large coupling between the motion and external systems for efficient readout and manipulation. Here, we report on a novel approach, in which we capacitively couple a high-Q graphene mechanical resonator (Q ≈ 10(5)) to a superconducting microwave cavity. The initial devices exhibit a large single-photon coupling of ∼10 Hz. Remarkably, we can electrostatically change the graphene equilibrium position and thereby tune the single photon coupling, the mechanical resonance frequency, and the sign and magnitude of the observed Duffing nonlinearity. The strong tunability opens up new possibilities, such as the tuning of the optomechanical coupling strength on a time scale faster than the inverse of the cavity line width. With realistic improvements, it should be possible to enter the regime of quantum optomechanics.

Self-organization of atoms along a nanophotonic waveguide.

Atoms coupled to nanophotonic interfaces represent an exciting frontier for the investigation of quantum light-matter interactions. While most work has considered the interaction between statically positioned atoms and light, here we demonstrate that a wealth of phenomena can arise from the self-consistent interaction between atomic internal states, optical scattering, and atomic forces. We consider in detail the case of atoms coupled to a one-dimensional nanophotonic waveguide and show that this interplay gives rise to the self-organization of atomic positions along the waveguide, which can be probed through distinct characteristics in the reflection and transmission spectra.

Single-photon nonlinear optics with graphene plasmons.

We show that it is possible to realize significant nonlinear optical interactions at the few photon level in graphene nanostructures. Our approach takes advantage of the electric field enhancement associated with the strong confinement of graphene plasmons and the large intrinsic nonlinearity of graphene. Such a system could provide a powerful platform for quantum nonlinear optical control of light. As an example, we consider an integrated optical device that exploits this large nonlinearity to realize a single photon switch.

Generation of single optical plasmons in metallic nanowires coupled to quantum dots.

Control over the interaction between single photons and individual optical emitters is an outstanding problem in quantum science and engineering. It is of interest for ultimate control over light quanta, as well as for potential applications such as efficient photon collection, single-photon switching and transistors, and long-range optical coupling of quantum bits. Recently, substantial advances have been made towards these goals, based on modifying photon fields around an emitter using high-finesse optical cavities. Here we demonstrate a cavity-free, broadband approach for engineering photon-emitter interactions via subwavelength confinement of optical fields near metallic nanostructures. When a single CdSe quantum dot is optically excited in close proximity to a silver nanowire, emission from the quantum dot couples directly to guided surface plasmons in the nanowire, causing the wire's ends to light up. Non-classical photon correlations between the emission from the quantum dot and the ends of the nanowire demonstrate that the latter stems from the generation of single, quantized plasmons. Results from a large number of devices show that efficient coupling is accompanied by more than 2.5-fold enhancement of the quantum dot spontaneous emission, in good agreement with theoretical predictions.

Cavity opto-mechanics using an optically levitated nanosphere.

Recently, remarkable advances have been made in coupling a number of high-Q modes of nano-mechanical systems to high-finesse optical cavities, with the goal of reaching regimes in which quantum behavior can be observed and leveraged toward new applications. To reach this regime, the coupling between these systems and their thermal environments must be minimized. Here we propose a novel approach to this problem, in which optically levitating a nano-mechanical system can greatly reduce its thermal contact, while simultaneously eliminating dissipation arising from clamping. Through the long coherence times allowed, this approach potentially opens the door to ground-state cooling and coherent manipulation of a single mesoscopic mechanical system or entanglement generation between spatially separate systems, even in room-temperature environments. As an example, we show that these goals should be achievable when the mechanical mode consists of the center-of-mass motion of a levitated nanosphere.

Nanoplasmonic lattices for ultracold atoms.

We propose to use subwavelength confinement of light associated with the near field of plasmonic systems to create nanoscale optical lattices for ultracold atoms. Our approach combines the unique coherence properties of isolated atoms with the subwavelength manipulation and strong light-matter interaction associated with nanoplasmonic systems. It allows one to considerably increase the energy scales in the realization of Hubbard models and to engineer effective long-range interactions in coherent and dissipative many-body dynamics. Realistic imperfections and potential applications are discussed.

Enhancement of mechanical Q factors by optical trapping.

The quality factor of a mechanical resonator is an important figure of merit for various sensing applications and for observing quantum behavior. Here, we demonstrate a technique to push the quality factor of a micromechanical resonator beyond conventional material and fabrication limits by using an optical field to stiffen or trap a particular motional mode. Optical forces increase the oscillation frequency by storing most of the mechanical energy in a nearly lossless optical potential, thereby strongly diluting the effect of material dissipation. By placing a 130 nm thick SiO2 pendulum in an optical standing wave, we achieve an increase in the pendulum center-of-mass frequency from 6.2 to 145 kHz. The corresponding quality factor increases 50-fold from its intrinsic value to a final value of Q=5.8(1.1)×10(5), representing more than an order of magnitude improvement over the conventional limits of SiO2 for this geometry. Our technique may enable new opportunities for mechanical sensing and facilitate observations of quantum behavior in this class of mechanical systems.

Origins of All-Optical Generation of Plasmons in Graphene.

Graphene, despite its centrosymmetric structure, is predicted to have a substantial second order nonlinearity, arising from non-local effects. However, there is disagreement between several published theories and experimental data. Here we derive an expression for the second order conductivity of graphene in the non-local regime using perturbation theory, concentrating on the difference frequency mixing process, and compare our results with those already published. We find a second-order conductivity (σ(2) ≈ 10-17 AmV-2) that is approximately three orders of magnitude less than that estimated from recent experimental results. This indicates that nonlinear optical coupling to plasmons in graphene cannot be described perturbatively through the electronic nonlinearity, as previously thought. We also show that this discrepancy cannot be attributed to the bulk optical nonlinearity of the substrate. As a possible alternative, we present a simple theoretical model of how a non-linearity can arise from photothermal effects, which generates a field at least two orders of magnitude larger than that found from perturbation theory.

Intensity dependences of the nonlinear optical excitation of plasmons in graphene.

Recently, we demonstrated an all-optical coupling scheme for plasmons, which takes advantage of the intrinsic nonlinear optical response of graphene. Frequency mixing using free-space, visible light pulses generates surface plasmons in a planar graphene sample, where the phase matching condition can define both the wavevector and energy of surface waves and intraband transitions. Here, we also show that the plasmon generation process is strongly intensity-dependent, with resonance features washed out for absorbed pulse fluences greater than 0.1 J m-2 This implies a subtle interplay between the nonlinear generation process and sample heating. We discuss these effects in terms of a non-equilibrium charge distribution using a two-temperature model.This article is part of the themed issue 'New horizons for nanophotonics'.

Limited joint mobility in power lifters.

In this study we compared the flexibility of 10 power lifters with 10 age-matched nonpower lifters as controls. To do this, we used goniometric measurements, the behind the back reach test, and the sit and reach test. The sit and reach test was the only measurement that showed the flexibility of the power lifters to be greater than that of the nonpower lifters.

Influence of gender and age on the behind-the-back reach test.

The behind-the-back reach test is a reproducible and reliable physical fitness test for musculoskeletal extensibility of the upper extremities, shoulder girdles, and upper back. Requiring only a rigid ruler and marking pen, administration of this test can be learned easily both by medical and nonmedical personnel. Normative data derived from a study of healthy subjects of different ages demonstrated that extensibility decreases with age. Moreover, musculoskeletal extensibility for women was significantly greater than that for men. The test results were not influenced significantly by anthropometric measurements.