Frustration elimination for effective optical spins in coherent Ising machines

Frustration, that is, the impossibility to satisfy the energetic preferences between all spin pairs simultaneously, underlies the complexity of many fundamental properties in spin systems, including the computational hardness to determine their ground states. Coherent Ising machines (CIM) have been proposed as a promising analog computational approach to efficiently find different degenerate ground states of large and complex Ising models. However, CIMs also face challenges in solving frustrated Ising models: Frustration not only reduces the probability to find good solutions, but it also prohibits to leverage quantum effects in doing so. To circumvent these detrimental effects of frustration, we show how frustrated Ising models can be mapped to frustration-free CIM configurations by including ancillary modes and modifying the coupling protocol used in current CIM designs. In our proposal, degenerate optical parametric oscillator (DOPO) modes encode the ground state candidates of the studied Ising model, while the ancillary modes enable the autonomous transformation to a frustration-free Ising model that preserves the ground states encoded in the DOPO modes. Such frustration elimination may empower current CIMs to improve precision and to benefit from quantum effects in dealing with frustrated Ising models.Comment: 6 pages, 3 figure

Coherent-cluster-state generation in networks of degenerate optical parametric oscillators

Cluster states are versatile quantum resources and an essential building block for measurement-based quantum computing. The possibility to generate cluster states in specific systems may thus serve as an indicator if and to what extent these systems can be harnessed for quantum technologies and quantum information processing in particular. Here, we apply this analysis to networks of degenerate optical parametric oscillators (DOPOs), also called coherent Ising machines (CIMs). CIMs are distinguished by their highly flexible coupling capabilities, which makes it possible to use them, e.g., to emulate large spin systems. As CIMs typically operate with coherent states (and superpositions thereof), it is natural to consider cluster states formed by superpositions of coherent states, i.e., coherent cluster states. As we show, such coherent cluster states can, under ideal conditions, be generated in DOPO networks with the help of beam splitters and classical pumps. Our subsequent numerical analysis provides the minimum requirements for the generation of coherent cluster states under realistic conditions. Moreover, we discuss how nonequilibrium pumps can improve the generation of coherent cluster states. In order to assess the quality of the cluster state generation, we map the generated states to an effective spin space using modular variables, which allows us to apply entanglement criteria tailored for spin-based cluster states.Comment: 12 pages, 8 figure

Electronic coolers based on superconducting tunnel junctions: fundamentals and applications

International audienceThermo-electric transport at the nano-scale is a rapidly developing topic, in particular in superconductor-based hybrid devices. In this review paper, we first discuss the fundamental principles of electronic cooling in mesoscopic superconducting hybrid structures, the related limitations and applications. We review recent work performed in Grenoble on the effects of Andreev reflection, photonic heat transport, phonon cooling, as well as on an innovative fabrication technique for powerful coolers

High flux cold Rubidium atomic beam for strongly coupled Cavity QED

This paper presents a setup capable of producing a high-flux continuous beam of cold rubidium atoms for cavity QED experiments in the regime of strong coupling. A 2 $D^+$ MOT, loaded by rubidium getters in a dry film coated vapor cell, fed a secondary moving-molasses MOT (MM-MOT) at a rate of 1.5 x $10^{10}$ atoms/sec. The MM-MOT provided a continuous beam with tunable velocity. This beam was then directed through the waist of a 280 $\mu$m cavity resulting in a Rabi splitting of more than +/- 10 MHz. The presence of sufficient number of atoms in the cavity mode also enabled splitting in the polarization perpendicular to the input. The cavity was in the strong coupling regime, with parameters (g, $\kappa$, $\gamma$)/2$\pi$ equal to (7, 3, 6)/ 2$\pi$ MHz.Comment: Journal pape

Design and Vertical Tests of SPS-series Double-Quarter Wave (DQW) Cavity Prototypes for the HL-LHC Crab Cavity System

Crab crossing is essential for high-luminosity colliders. The High Luminosity Large Hadron Collider (HL-LHC) will equip one of its Interaction Points (IP1) with Double-Quarter Wave (DQW) crab cavities. A DQW cavity is a new generation of deflecting RF cavities that stands out for its compactness and broad frequency separation between fundamental and first high-order modes. The deflecting kick is provided by its fundamental mode. Each HL-LHC DQW cavity shall provide a nominal deflecting voltage of 3.4 MV, although up to 5.0 MV may be required. A Proof-of-Principle (PoP) DQW cavity was limited by quench at 4.6 MV. This paper describes a new, highly optimized cavity, designated DQW SPS-series, which satisfies dimensional, cryogenic, manufacturing and impedance requirements for beam tests at SPS and operation in LHC. Two prototypes of this DQW SPS-series were fabricated by US industry and cold tested after following conventional SRF surface treatment. Both units outperformed the PoP cavity, reaching a deflecting voltage of 5.3-5.9 MV. This voltage - the highest reached by a DQW cavity - is well beyond the nominal voltage of 3.4 MV and may even operate at the ultimate voltage of 5.0MVwith sufficient margin. This paper covers fabrication, surface preparation and cryogenic RF test results and implications

Two-Level Atom in an Optical Parametric Oscillator: Spectra of Transmitted and Fluorescent Fields in the Weak Driving Field Limit

We consider the interaction of a two-level atom inside an optical parametric oscillator. In the weak driving field limit, we essentially have an atom-cavity system driven by the occasional pair of correlated photons, or weakly squeezed light. We find that we may have holes, or dips, in the spectrum of the fluorescent and transmitted light. This occurs even in the strong-coupling limit when we find holes in the vacuum-Rabi doublet. Also, spectra with a sub-natural linewidth may occur. These effects disappear for larger driving fields, unlike the spectral narrowing obtained in resonance fluorescence in a squeezed vacuum; here it is important that the squeezing parameter $N$ tends to zero so that the system interacts with only one correlated pair of photons at a time. We show that a previous explanation for spectral narrowing and spectral holes for incoherent scattering is not applicable in the present case, and propose a new explanation. We attribute these anomalous effects to quantum interference in the two-photon scattering of the system.Comment: 10 pages, 17 figures, submitted to Phys Rev

Glycaemic control and risk of incident urinary incontinence in women with Type 1 diabetes: results from the Diabetes Control and Complications Trial and Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) study

AimsTo study the impact of glycaemic control on urinary incontinence in women who participated in the Diabetes Control and Complications Trial (DCCT; 1983–1993) and its observational follow‐up study, the Epidemiology of Diabetes Interventions and Complications (EDIC; 1994–present).MethodsStudy participants were women who completed, at both years 10 (2003) and 17 (2010) of the EDIC follow‐up, the urological assessment questionnaire (UroEDIC). Urinary incontinence was defined as self‐reported involuntary leakage of urine that occurred at least weekly. Incident urinary incontinence was defined as weekly urinary incontinence present at EDIC year 17 but not at EDIC year 10. Multivariable regression models were used to examine the association of incident urinary incontinence with comorbid prevalent conditions and glycaemic control (mean HbA1c over the first 10 years of EDIC).ResultsA total of 64 (15.3%) women with Type 1 diabetes (mean age 43.6 ± 6.3 years at EDIC year 10) reported incident urinary incontinence at EDIC year 17. When adjusted for clinical covariates (including age, DCCT cohort assignment, DCCT treatment arm, BMI, insulin dosage, parity, hysterectomy, autonomic neuropathy and urinary tract infection in the last year), the mean EDIC HbA1c was associated with increased odds of incident urinary incontinence (odds ratio 1.03, 95% CI 1.01–1.06 per mmol/mol increase; odds ratio 1.41, 95% CI 1.07–1.89 per % HbA1c increase).ConclusionsIncident urinary incontinence was associated with higher HbA1c levels in women with Type 1 diabetes, independent of other recognized risk factors. These results suggest the potential for women to modify their risk of urinary incontinence with improved glycaemic control. (Clinical Trials Registry no: NCT00360815 and NCT00360893).What’s new?Research to date has failed to show an association between glycaemic control and urinary incontinence (UI) in women with diabetes.We examined the relationship between HbA1c and UI using longitudinal data from the Diabetes Control and Complications Trial (DCCT) and its observational follow‐up, the Epidemiology of Diabetes Interventions and Complications (EDIC) study.Our findings show that the odds of UI increase with poor glycaemic control in women with Type 1 diabetes, independently of other well‐described predictors of UI.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134490/1/dme13126.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134490/2/dme13126_am.pd

Direct measurement of three-body interactions

Three-body interactions have been measured among three charged colloidal particles in deionized solvent. Two of the particles have been confined to an optical line-trap while the third one was approached by means of a focused laser beam. The experimentally determined three-body interactions are attractive and roughly of the same magnitude and range as the pair-interactions. In addition, numerical calculations have been performed, which show good agreement with the experimental results

Risk factors associated with typhoid fever in children aged 2-16 years in Karachi, Pakistan

We analysed the data from the control group in a typhoid vaccine trial in Karachi to assess the differences in individual-, household-and cluster-level characteristics for developing typhoid fever. The annual incidence of typhoid in children aged 2-16 years in the control arm of the vaccine trial was 151/100 000 population. After adjustment, the risk of typhoid was lower with increasing age [risk ratio (RR) 0.89, 95% confidence interval (CI) 0.83-0.95], was higher with an increase in population density (RR 1.13, 95% CI 1.05-1.21) and was lower in the households using a safe drinking-water source (RR 0.63, 95% CI 0.41-0.99). Typhoid fever affects younger children living in areas of high population density and lack of access to safe water in Pakistan. A combination of environmental and biological interventions is required to prevent the continued epidemiological and economic impact of typhoid fever in high-risk areas of Pakistan