62 research outputs found
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
() and efficient luminescence extraction ( 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 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 9â32 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 ictalâonset zone near or within DCSâmapped 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 schoolâaged 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 Qâs 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 kĂ€llen isolerad i kisel. Denna upptĂ€ckt Ă€r av stort intresse för kvantteknologier p.g.a. kisels förmĂ„ga gĂ€llande integration och skalbarhet. G-centers spontana rekombinationshastighet behöver dock kontrolleras för att skapa en anvĂ€ndbar enfoton kĂ€lla. Det kan göras genom Purcell-effekten i en optisk resonator. Som ett första steg har vi studerat mikroresonatorer som innehĂ„ller G-center i det presenterade projektet, med flera mĂ„l: utvĂ€rdering av kvalitetsfaktor för mikroresonatorer som innehĂ„ller G-center, demonstration av optisk aktivitet av G-center efter tillverkning av kiselmikrostrukturer, och utvĂ€rdering av deras potential för integrerade mikrolaser pĂ„ SOI. Observation av stark fotoluminescens av G-center och resonatormoder med stor-Q bekrĂ€ftar kompatibilitet mellan G-center och vanliga steg för bearbetning av kisel, och Ă€r uppmuntrande för framtida Kvantum Optik experimenter med isolerade G-center i mikroresonatorer. Resultaten visar att ljusförstĂ€rkning troligtvis börjar, men absorption av andra defekter mĂ„ste minskas för att uppnĂ„ 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 Qâs 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 kĂ€llen isolerad i kisel. Denna upptĂ€ckt Ă€r av stort intresse för kvantteknologier p.g.a. kisels förmĂ„ga gĂ€llande integration och skalbarhet. G-centers spontana rekombinationshastighet behöver dock kontrolleras för att skapa en anvĂ€ndbar enfoton kĂ€lla. Det kan göras genom Purcell-effekten i en optisk resonator. Som ett första steg har vi studerat mikroresonatorer som innehĂ„ller G-center i det presenterade projektet, med flera mĂ„l: utvĂ€rdering av kvalitetsfaktor för mikroresonatorer som innehĂ„ller G-center, demonstration av optisk aktivitet av G-center efter tillverkning av kiselmikrostrukturer, och utvĂ€rdering av deras potential för integrerade mikrolaser pĂ„ SOI. Observation av stark fotoluminescens av G-center och resonatormoder med stor-Q bekrĂ€ftar kompatibilitet mellan G-center och vanliga steg för bearbetning av kisel, och Ă€r uppmuntrande för framtida Kvantum Optik experimenter med isolerade G-center i mikroresonatorer. Resultaten visar att ljusförstĂ€rkning troligtvis börjar, men absorption av andra defekter mĂ„ste minskas för att uppnĂ„ 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
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