Dynamical control of quantum heat engines using exceptional points.

A quantum thermal machine is an open quantum system coupled to hot and cold thermal baths. Thus, its dynamics can be well understood using the concepts and tools from non-Hermitian quantum systems. A hallmark of non-Hermiticity is the existence of exceptional points where the eigenvalues of a non-Hermitian Hamiltonian or a Liouvillian superoperator and their associated eigenvectors coalesce. Here, we report the experimental realization of a single-ion heat engine and demonstrate the effect of Liouvillian exceptional points on the dynamics and the performance of a quantum heat engine. Our experiments have revealed that operating the engine in the exact- and broken-phases, separated by a Liouvillian exceptional point, respectively during the isochoric heating and cooling strokes of an Otto cycle produces more work and output power and achieves higher efficiency than executing the Otto cycle completely in the exact phase where the system has an oscillatory dynamics and higher coherence. This result opens interesting possibilities for the control of quantum heat engines and will be of interest to other research areas that are concerned with the role of coherence and exceptional points in quantum processes and in work extraction by thermal machines.

Large Collective Lamb Shift of Two Distant Superconducting Artificial Atoms.

Virtual photons can mediate interaction between atoms, resulting in an energy shift known as a collective Lamb shift. Observing the collective Lamb shift is challenging, since it can be obscured by radiative decay and direct atom-atom interactions. Here, we place two superconducting qubits in a transmission line terminated by a mirror, which suppresses decay. We measure a collective Lamb shift reaching 0.8% of the qubit transition frequency and twice the transition linewidth. We also show that the qubits can interact via the transmission line even if one of them does not decay into it.

Acoustic Radiation Force and Torque on Small Particles as Measures of the Canonical Momentum and Spin Densities.

We examine acoustic radiation force and torque on a small (subwavelength) absorbing isotropic particle immersed in a monochromatic (but generally inhomogeneous) sound-wave field. We show that by introducing the monopole and dipole polarizabilities of the particle, the problem can be treated in a way similar to the well-studied optical forces and torques on dipole Rayleigh particles. We derive simple analytical expressions for the acoustic force (including both the gradient and scattering forces) and torque. Importantly, these expressions reveal intimate relations to the fundamental field properties introduced recently for acoustic fields: the canonical momentum and spin angular momentum densities. We compare our analytical results with previous calculations and exact numerical simulations. We also consider an important example of a particle in an evanescent acoustic wave, which exhibits the mutually orthogonal scattering (radiation-pressure) force, gradient force, and torque from the transverse spin of the field.

Spin-Hall effect of light at a tilted polarizer.

We describe the spin-Hall effect of light (as well as the angular Goos-Hänchen effect) at a tilted linear-dichroic plate, such as a usual linear polarizer. Although the spin-Hall effect at a tilted polarizer was previously associated with the geometric spin-Hall effect of light (which was contrasted to the regular spin-Hall effect) [Phys. Rev. Lett.112, 113902 (2014) PRLTAO0031-900710.1103/PhysRevLett.112.113902], we show that the effect is actually an example of the regular spin-Hall effect that occurs at tilted anisotropic plates [Optica3, 1039 (2016) OPTIC82334-253610.1364/OPTICA.3.001039]. Moreover, our approach reveals the angular spin-Hall shift, which is absent in the "geometric" approach. We verify our theory experimentally using the method of quantum weak measurements.

Electromagnetic Helicity in Complex Media.

Optical helicity density is usually discussed for monochromatic electromagnetic fields in free space. It plays an important role in the interaction with chiral molecules or nanoparticles. Here we introduce the optical helicity density in a dispersive isotropic medium. Our definition is consistent with biorthogonal Maxwell electromagnetism in optical media and the Brillouin energy density as well as with the recently introduced canonical momentum and spin of light in dispersive media. We consider a number of examples, including electromagnetic waves in dielectrics, negative-index materials, and metals, as well as interactions of light in a medium with chiral and magnetoelectric molecules.

Electric-current-induced unidirectional propagation of surface plasmon-polaritons.

Nonreciprocity and one-way propagation of optical signals are crucial for modern nanophotonic technology, and typically achieved using magneto-optical effects requiring large magnetic biases. Here we suggest a fundamentally novel approach to achieve unidirectional propagation of surface plasmon-polaritons (SPPs) at metal-dielectric interfaces. We employ a direct electric current in metals, which produces a Doppler frequency shift of SPPs due to the uniform drift of electrons. This tilts the SPP dispersion, enabling one-way propagation, as well as zero and negative group velocities. The results are demonstrated for planar interfaces and cylindrical nanowire waveguides.

Reflective Amplification without Population Inversion from a Strongly Driven Superconducting Qubit.

Amplification of optical or microwave fields is often achieved by strongly driving a medium to induce population inversion such that a weak probe can be amplified through stimulated emission. Here we strongly couple a superconducting qubit, an artificial atom, to the field in a semi-infinite waveguide. When driving the qubit strongly on resonance such that a Mollow triplet appears, we observe a 7% amplitude gain for a weak probe at frequencies in between the triplet. This amplification is not due to population inversion, neither in the bare qubit basis nor in the dressed-state basis, but instead results from a four-photon process that converts energy from the strong drive to the weak probe. We find excellent agreement between the experimental results and numerical simulations without any free fitting parameters. Since our device consists of a single two-level artificial atom, the simplest possible quantum system, it can be viewed as the most fundamental version of a four-wave-mixing parametric amplifier.

Hole Spin Resonance and Spin-Orbit Coupling in a Silicon Metal-Oxide-Semiconductor Field-Effect Transistor.

We study hole spin resonance in a p-channel silicon metal-oxide-semiconductor field-effect transistor. In the subthreshold region, the measured source-drain current reveals a double dot in the channel. The observed spin resonance spectra agree with a model of strongly coupled two-spin states in the presence of a spin-orbit-induced anticrossing. Detailed spectroscopy at the anticrossing shows a suppressed spin resonance signal due to spin-orbit-induced quantum state mixing. This suppression is also observed for multiphoton spin resonances. Our experimental observations agree with theoretical calculations.

Anomalous time delays and quantum weak measurements in optical micro-resonators.

Quantum weak measurements, wavepacket shifts and optical vortices are universal wave phenomena, which originate from fine interference of multiple plane waves. These effects have attracted considerable attention in both classical and quantum wave systems. Here we report on a phenomenon that brings together all the above topics in a simple one-dimensional scalar wave system. We consider inelastic scattering of Gaussian wave packets with parameters close to a zero of the complex scattering coefficient. We demonstrate that the scattered wave packets experience anomalously large time and frequency shifts in such near-zero scattering. These shifts reveal close analogies with the Goos-Hänchen beam shifts and quantum weak measurements of the momentum in a vortex wavefunction. We verify our general theory by an optical experiment using the near-zero transmission (near-critical coupling) of Gaussian pulses propagating through a nano-fibre with a side-coupled toroidal micro-resonator. Measurements demonstrate the amplification of the time delays from the typical inverse-resonator-linewidth scale to the pulse-duration scale.

Observation of non-Hermitian degeneracies in a chaotic exciton-polariton billiard.

Exciton-polaritons are hybrid light-matter quasiparticles formed by strongly interacting photons and excitons (electron-hole pairs) in semiconductor microcavities. They have emerged as a robust solid-state platform for next-generation optoelectronic applications as well as for fundamental studies of quantum many-body physics. Importantly, exciton-polaritons are a profoundly open (that is, non-Hermitian) quantum system, which requires constant pumping of energy and continuously decays, releasing coherent radiation. Thus, the exciton-polaritons always exist in a balanced potential landscape of gain and loss. However, the inherent non-Hermitian nature of this potential has so far been largely ignored in exciton-polariton physics. Here we demonstrate that non-Hermiticity dramatically modifies the structure of modes and spectral degeneracies in exciton-polariton systems, and, therefore, will affect their quantum transport, localization and dynamical properties. Using a spatially structured optical pump, we create a chaotic exciton-polariton billiard--a two-dimensional area enclosed by a curved potential barrier. Eigenmodes of this billiard exhibit multiple non-Hermitian spectral degeneracies, known as exceptional points. Such points can cause remarkable wave phenomena, such as unidirectional transport, anomalous lasing/absorption and chiral modes. By varying parameters of the billiard, we observe crossing and anti-crossing of energy levels and reveal the non-trivial topological modal structure exclusive to non-Hermitian systems. We also observe mode switching and a topological Berry phase for a parameter loop encircling the exceptional point. Our findings pave the way to studies of non-Hermitian quantum dynamics of exciton-polaritons, which may uncover novel operating principles for polariton-based devices.

Loss-induced suppression and revival of lasing.

Controlling and reversing the effects of loss are major challenges in optical systems. For lasers, losses need to be overcome by a sufficient amount of gain to reach the lasing threshold. In this work, we show how to turn losses into gain by steering the parameters of a system to the vicinity of an exceptional point (EP), which occurs when the eigenvalues and the corresponding eigenstates of a system coalesce. In our system of coupled microresonators, EPs are manifested as the loss-induced suppression and revival of lasing. Below a critical value, adding loss annihilates an existing Raman laser. Beyond this critical threshold, lasing recovers despite the increasing loss, in stark contrast to what would be expected from conventional laser theory. Our results exemplify the counterintuitive features of EPs and present an innovative method for reversing the effect of loss.

Brownian transport in corrugated channels with inertia.

Transport of suspended Brownian particles dc driven along corrugated narrow channels is numerically investigated in the regime of finite damping. We show that inertial corrections cannot be neglected as long as the width of the channel bottlenecks is smaller than an appropriate particle diffusion length, which depends on the the channel corrugation and the drive intensity. With such a diffusion length being inversely proportional to the damping constant, transport through sufficiently narrow obstructions turns out to be always sensitive to the viscosity of the suspension fluid. The inertia corrections to the transport quantifiers, mobility, and diffusivity markedly differ for smoothly and sharply corrugated channels.

Driven Brownian transport through arrays of symmetric obstacles.

We numerically investigate the transport of a suspended overdamped Brownian particle which is driven through a two-dimensional rectangular array of circular obstacles with finite radius. Two limiting cases are considered in detail, namely, when the constant drive is parallel to the principal or the diagonal array axes. This corresponds to studying the Brownian transport in periodic channels with reflecting walls of different topologies. The mobility and diffusivity of the transported particles in such channels are determined as functions of the drive and the array geometric parameters. Prominent transport features, like negative differential mobilities, excess diffusion peaks, and unconventional asymptotic behaviors, are explained in terms of two distinct lengths, the size of single obstacles (trapping length), and the lattice constant of the array (local correlation length). Local correlation effects are further analyzed by continuously rotating the drive between the two limiting orientations.

Observation of the dynamical Casimir effect in a superconducting circuit.

One of the most surprising predictions of modern quantum theory is that the vacuum of space is not empty. In fact, quantum theory predicts that it teems with virtual particles flitting in and out of existence. Although initially a curiosity, it was quickly realized that these vacuum fluctuations had measurable consequences--for instance, producing the Lamb shift of atomic spectra and modifying the magnetic moment of the electron. This type of renormalization due to vacuum fluctuations is now central to our understanding of nature. However, these effects provide indirect evidence for the existence of vacuum fluctuations. From early on, it was discussed whether it might be possible to more directly observe the virtual particles that compose the quantum vacuum. Forty years ago, it was suggested that a mirror undergoing relativistic motion could convert virtual photons into directly observable real photons. The phenomenon, later termed the dynamical Casimir effect, has not been demonstrated previously. Here we observe the dynamical Casimir effect in a superconducting circuit consisting of a coplanar transmission line with a tunable electrical length. The rate of change of the electrical length can be made very fast (a substantial fraction of the speed of light) by modulating the inductance of a superconducting quantum interference device at high frequencies (>10 gigahertz). In addition to observing the creation of real photons, we detect two-mode squeezing in the emitted radiation, which is a signature of the quantum character of the generation process.

Gastric endocrine tumors type I: treatment with long-acting somatostatin analogs.

Gastric endocrine tumors associated with autoimmune chronic atrophic gastritis (gastric carcinoid type I) are almost exclusively benign lesions with little risk of deep invasion of the gastric parietal wall. For this reason, the role of octreotide in the treatment of these neoplastic lesions is controversial. Nine patients with more than five type I gastric endocrine tumors each <1 cm in size, without invasion of the muscularis propria and with Ki-67 index lower than 3%, were treated with long-acting somatostatin analogs for 12 months. After 6 months and again after 12 months, all the patients underwent upper gastrointestinal (GI) endoscopy with multiple biopsies. The plasma chromogranin A (CgA) levels and the gastrin levels in the serum were also determined. In all patients, the gastric neoplastic lesions disappeared after 12 months of somatostatin analog therapy. We also observed a significant reduction of CgA and gastrin levels at 6 and at 12 months of therapy as compared with the baseline values. We demonstrate that somatostatin analog treatment provokes the pathological regression of type I gastric carcinoids. This therapeutic approach should be considered as a valid option in selected patients with multiple type I gastric endocrine tumors.

The possible role of endocrine disrupting chemicals in the aetiology of cryptorchidism and hypospadias: a population-based case-control study in rural Sicily.

Abstract This was an open case-control study of the possible association between parental occupational and domestic exposures to potential endocrine disrupting chemicals (EDC) assessed by questionnaire and cryptorchidism and hypospadias in their offspring in the agricultural area of Ragusa. Cases of infants born between 1998 and 2002 with either of these two malformations (n=90), and controls (n=203), were recruited through the paediatric services (for cases) and a random sample of healthy infants attending the same services born in the same period of time (for controls). Data on occupational and environmental exposures of parents prior to and during the index case (or control), were collected through interviews with both parents. Concerning occupational exposures, we did not find a statistically significant increase in risk among parents directly involved in agricultural work. We did find a non-statistically significant increase in risk for cryptorchidism in mothers employed in agriculture [adjusted odds ratios (OR) 2.97; 95% confidence interval (CI) 0.77-11.47] and with probable exposure to pesticides (adjusted OR 2.74; 95% CI 0.72-10.42). Fathers who had indirect contact with agricultural products (transport and retail) had an increased risk (not statistically significant) for cryptorchidism (adjusted OR 2.45; 95% CI 0.63-9.59) and hypospadias and cryptorchidism combined (adjusted OR 2.24; 95% CI 0.67-7.48). Increases in risk of the two malformations pooled were also observed in relation to the mother's age below 25 (adjusted OR 1.99; 95% CI 0.97-4.09), to the presence of genital disease of the father (adjusted OR 2.41; 95%C I0.94-6.17), and the mother (adjusted OR 3.47;95% CI 1.34-8.99), to low birth weight of the infant (adjusted OR 4.49; 95% CI 1.23-16.31). Increased risk was also observed for mothers consuming alcohol during pregnancy (adjusted OR 3.09; 95% CI 0.98-9.66), and for couples who conceived while using condoms (adjusted OR 2.12; 95% CI 1.02-4.41). The study therefore provides only limited support to the hypothesis of a possible association between the risk of cryptorchidism and hypospadias and the occupational exposure to EDC and agricultural work.

Fluctuation-induced casimir forces in granular fluids.

We numerically investigate the behavior of driven noncohesive granular media and find that two fixed large intruder particles, immersed in a sea of small particles, experience, in addition to a short-range depletion force, a long-range repulsive force. The observed long-range interaction is fluctuation-induced and we propose a mechanism similar to the Casimir effect that generates it: The hydrodynamic fluctuations are geometrically confined between the intruders, producing an unbalanced renormalized pressure. An estimation based on computing the possible Fourier modes explains the repulsive force and is in qualitative agreement with the simulations.

Cryptorchidism and hypospadias in the Sicilian district of Ragusa and the use of pesticides.

The aim of the study was to explore the role of environmental exposures to pesticides in the birth prevalence of hypospadias and cryptorchidism, in the 12 agricultural municipalities of Ragusa Sicily. Data on the birth prevalence of the two birth defects were obtained from the local pediatric services for the period 1998-2002. Municipalities were ranked according to the degree of "pesticide impact" on the basis of three quantitative criteria of intensity of agricultural activities of the population. We found a significantly higher birth prevalence of hypospadias with increasing "pesticide impact" (trend test, P=0.003). The association with cryptorchidism was not statistically significant, but when the two birth defects were pooled together, the linear trend was significant (trend test, P=0.001).

Endocrine pancreatic tumors: factors correlated with survival.

BACKGROUND: The aim of this study was to evaluate the survival rate of patients with endocrine tumors of the pancreas, functioning or non-functioning, associated or not with MEN 1 syndrome. PATIENTS AND METHODS: Eighty-three patients with pancreatic endocrine tumors diagnosed in our department from 1978 to 2003 were studied. RESULTS: The study included 37 men (44.6%) and 46 women (55.4%). The median age of patients at diagnosis was 55 years (range 19-81 years). Fifty-two patients (62.7%) had non-functioning endocrine tumors, 16 (19.3%) had functioning endocrine tumors and 15 (18.1%) had MEN 1 disease with pancreatic involvement. Twenty-seven patients (32.5%) had liver metastases at the time of diagnosis, involvement of the lymph nodes was found in 47 out of 79 patients (59.5%). Forty patients (48.2%) had radical surgery, 20 (24.1%) had palliative surgery and 53 were treated medically. The survival rate was significantly related to the presence of metastases, lymph node involvement, and the type of tumor and treatment. CONCLUSIONS: Tumor resection, the absence of liver and lymph node metastases, and the presence of MEN 1 syndrome are related to a better survival rate. Radical surgery continues to have a central role in the therapeutic approach to endocrine tumors of the pancreas.