Parallelizable Synthesis of Arbitrary Single-Qubit Gates with Linear Optics and Time-Frequency Encoding

We propose novel methods for the exact synthesis of single-qubit unitaries with high success probability and gate fidelity, considering both time-bin and frequency-bin encodings. The proposed schemes are experimentally implementable with a spectral linear-optical quantum computation (S- LOQC) platform, composed of electro-optic phase modulators and phase-only programmable filters (pulse shapers). We assess the performances in terms of fidelity and probability of the two simplest 3-components configurations for arbitrary gate generation in both encodings and give an exact analytical solution for the synthesis of an arbitrary single-qubit unitary in the time-bin encoding, using a single-tone Radio Frequency (RF) driving of the EOMs. We further investigate the parallelization of arbitrary single-qubit gates over multiple qubits with a compact experimental setup, both for spectral and temporal encodings. We systematically evaluate and discuss the impact of the RF bandwidth - that conditions the number of tones driving the modulators - and of the choice of encoding for different targeted gates. We moreover quantify the number of high fidelity Hadamard gates that can be synthesized in parallel, with minimal and increasing resources in terms of driving RF tones in a realistic system. Our analysis positions spectral S-LOQC as a promising platform to conduct massively parallel single qubit operations, with potential applications to quantum metrology and quantum tomography.Comment: 21 pages, 6 figure

Purcell enhancement of silicon W centers in circular Bragg grating cavities

Generating single photons on demand in silicon is a challenge to the scalability of silicon-on-insulator integrated quantum photonic chips. While several defects acting as artificial atoms have recently demonstrated an ability to generate antibunched single photons, practical applications require tailoring of their emission through quantum cavity effects. In this work, we perform cavity quantum electrodynamics experiments with ensembles of artificial atoms embedded in silicon-on-insulator microresonators. The emitters under study, known as W color centers, are silicon tri-interstitial defects created upon self-ion implantation and thermal annealing. The resonators consist of circular Bragg grating cavities, designed for moderate Purcell enhancement ($F_p=12.5$) and efficient luminescence extraction ($\eta_{coll}=40\%$ for a numerical aperture of 0.26) for W centers located at the mode antinode. When the resonant frequency mode of the cavity is tuned with the zero-phonon transition of the emitters at 1218 nm, we observe a 20-fold enhancement of the zero-phonon line intensity, together with a two-fold decrease of the total relaxation time in time-resolved photoluminescence experiments. Based on finite-difference time-domain simulations, we propose a detailed theoretical analysis of Purcell enhancement for an ensemble of W centers, considering the overlap between the emitters and the resonant cavity mode. We obtain a good agreement with our experimental results assuming a quantum efficiency of $65 \pm 10 \%$ for the emitters in bulk silicon. Therefore, W centers open promising perspectives for the development of on-demand sources of single photons, harnessing cavity quantum electrodynamics in silicon photonic chips

Language mapping with navigated transcranial magnetic stimulation in pediatric and adult patients undergoing epilepsy surgery: Comparison with extraoperative direct cortical stimulation

Summary Objective Navigated transcranial magnetic stimulation (nTMS) is becoming increasingly popular in noninvasive preoperative language mapping, as its results correlate well enough with those obtained by direct cortical stimulation (DCS) during awake surgery in adult patients with tumor. Reports in the context of epilepsy surgery or extraoperative DCS in adults are, however, sparse, and validation of nTMS with DCS in children is lacking. Furthermore, little is known about the risk of inducing epileptic seizures with nTMS in pediatric epilepsy patients. We provide the largest validation study to date in an epilepsy surgery population. Methods We compared language mapping with nTMS and extraoperative DCS in 20 epilepsy surgery patients (age range 9‐32 years; 14 children and adolescents). Results In comparison with DCS, sensitivity of nTMS was 68 specificity 76 positive predictive value 27 and negative predictive value 95 Age, location of ictal‐onset zone near or within DCS‐mapped language areas or severity of cognitive deficits had no significant effect on these values. None of our patients had seizures during nTMS. Significance Our study suggests that nTMS language mapping is clinically useful and safe in epilepsy surgery patients, including school‐aged children and patients with extensive cognitive dysfunction. Similar to in tumor surgery, mapping results in the frontal region are most reliable. False negative findings may be slightly more likely in epilepsy than in tumor surgery patients. Mapping results should always be verified by other methods in individual patients.Peer reviewe

Gastroparesis and functional dyspepsia: excerpts from the AGA/ANMS meeting

Despite the relatively high prevelance of gastroparesis and functional dyspepsia, the aetiology and pathophysiology of these disorders remain incompletely understood. Similarly, the diagnostic and treatment options for these two disorders are relatively limited despite recent advances in our understanding of both disorders.This manuscript reviews the advances in the understanding of the epidemiology, pathophysiology, diagnosis, and treatment of gastroparesis and functional dyspepsia as discussed at a recent conference sponsored by the American Gastroenterological Association (AGA) and the American Neurogastroenterology and Motility Society (ANMS). Particular focus is placed on discussing unmet needs and areas for future research.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78690/1/j.1365-2982.2009.01434.x.pd

Optisk Studie av Mikroresonatorer med G-centra som Aktivt Medium

The G-center has recently been identified as the first deterministic single-photon punctual emitter isolated in silicon. This discovery is of great interest for largescale quantum technologies, due to the abilities of silicon in terms of integration and scalability. However, the spontaneous emission rate of the G-center still needs to be controlled in order to engineer a useful Single-Photon Source. This could be achieved by incorporating a single G-center in resonant microcavities to benefit from the Purcell effect. As a first step in this direction, we have studied in this project micro-cavities containing an ensemble of G-centers, more precisely Si micro-disks and micro-rings on oxide, with several objectives: the evaluation of the quality factor of micro-cavities containing G-centers, the demonstration of an optical activity of G-centers after the processing of the silicon micro-structures, and the evaluation of their potential as gain medium for integrated microlasers on SOI. The observation of bright photoluminescence from G-centers and of resonant cavity modes with Q’s in the few thousands range confirms the compatibility of G-centers with standard silicon processing steps, and is encouraging for future quantum optics experiments on isolated G centers in micro-cavities. Our results also tend to show that gain may be available in the material, but residual absorption still needs to be decreased to achieve lasing.G-center har nyligen identifierats som den första determinitiska ponctual enfoton källen isolerad i kisel. Denna upptäckt är av stort intresse för kvantteknologier p.g.a. kisels förmåga gällande integration och skalbarhet. G-centers spontana rekombinationshastighet behöver dock kontrolleras för att skapa en användbar enfoton källa. Det kan göras genom Purcell-effekten i en optisk resonator. Som ett första steg har vi studerat mikroresonatorer som innehåller G-center i det presenterade projektet, med flera mål: utvärdering av kvalitetsfaktor för mikroresonatorer som innehåller G-center, demonstration av optisk aktivitet av G-center efter tillverkning av kiselmikrostrukturer, och utvärdering av deras potential för integrerade mikrolaser på SOI. Observation av stark fotoluminescens av G-center och resonatormoder med stor-Q bekräftar kompatibilitet mellan G-center och vanliga steg för bearbetning av kisel, och är uppmuntrande för framtida Kvantum Optik experimenter med isolerade G-center i mikroresonatorer. Resultaten visar att ljusförstärkning troligtvis börjar, men absorption av andra defekter måste minskas för att uppnå laserregim

Optisk Studie av Mikroresonatorer med G-centra som Aktivt Medium

The G-center has recently been identified as the first deterministic single-photon punctual emitter isolated in silicon. This discovery is of great interest for largescale quantum technologies, due to the abilities of silicon in terms of integration and scalability. However, the spontaneous emission rate of the G-center still needs to be controlled in order to engineer a useful Single-Photon Source. This could be achieved by incorporating a single G-center in resonant microcavities to benefit from the Purcell effect. As a first step in this direction, we have studied in this project micro-cavities containing an ensemble of G-centers, more precisely Si micro-disks and micro-rings on oxide, with several objectives: the evaluation of the quality factor of micro-cavities containing G-centers, the demonstration of an optical activity of G-centers after the processing of the silicon micro-structures, and the evaluation of their potential as gain medium for integrated microlasers on SOI. The observation of bright photoluminescence from G-centers and of resonant cavity modes with Q’s in the few thousands range confirms the compatibility of G-centers with standard silicon processing steps, and is encouraging for future quantum optics experiments on isolated G centers in micro-cavities. Our results also tend to show that gain may be available in the material, but residual absorption still needs to be decreased to achieve lasing.G-center har nyligen identifierats som den första determinitiska ponctual enfoton källen isolerad i kisel. Denna upptäckt är av stort intresse för kvantteknologier p.g.a. kisels förmåga gällande integration och skalbarhet. G-centers spontana rekombinationshastighet behöver dock kontrolleras för att skapa en användbar enfoton källa. Det kan göras genom Purcell-effekten i en optisk resonator. Som ett första steg har vi studerat mikroresonatorer som innehåller G-center i det presenterade projektet, med flera mål: utvärdering av kvalitetsfaktor för mikroresonatorer som innehåller G-center, demonstration av optisk aktivitet av G-center efter tillverkning av kiselmikrostrukturer, och utvärdering av deras potential för integrerade mikrolaser på SOI. Observation av stark fotoluminescens av G-center och resonatormoder med stor-Q bekräftar kompatibilitet mellan G-center och vanliga steg för bearbetning av kisel, och är uppmuntrande för framtida Kvantum Optik experimenter med isolerade G-center i mikroresonatorer. Resultaten visar att ljusförstärkning troligtvis börjar, men absorption av andra defekter måste minskas för att uppnå laserregim

<title>Growth of Nd:GdLiF4 single crystals</title>

We report for the first time the growth of high quality single crystals of Nd doped GdLiF 4. We have revised the phase diagram of this system to search for optimum growth composition. The crystals were grown from a highly incongruent peritectic melt using the conventional weight-feed-back automatic diameter control Czochralski puller. Higher Nd doping (up to 4%) was achieved and the lasing performance was encouraging. We believe that the crystal has the potential to be used for diode pumped miniature laser applications

Growth Of Nd:Gdlif4 Single Crystals

We report for the first time the growth of high quality single crystals of Nd doped GdLiF 4. We have revised the phase diagram of this system to search for optimum growth composition. The crystals were grown from a highly incongruent peritectic melt using the conventional weight-feed-back automatic diameter control Czochralski puller. Higher Nd doping (up to 4%) was achieved and the lasing performance was encouraging. We believe that the crystal has the potential to be used for diode pumped miniature laser applications