Phase-locked indistinguishable photons with synthesized waveforms from a solid-state source

Resonance fluorescence in the Heitler regime provides access to single photons with coherence well beyond the Fourier transform limit of the transition, and holds the promise to circumvent environment-induced dephasing common to all solid-state systems. Here we demonstrate that the coherently generated single photons from a single self-assembled InAs quantum dot display mutual coherence with the excitation laser on a timescale exceeding 3 seconds. Exploiting this degree of mutual coherence we synthesize near-arbitrary coherent photon waveforms by shaping the excitation laser field. In contrast to post-emission filtering, our technique avoids both photon loss and degradation of the single photon nature for all synthesized waveforms. By engineering pulsed waveforms of single photons, we further demonstrate that separate photons generated coherently by the same laser field are fundamentally indistinguishable, lending themselves to creation of distant entanglement through quantum interference.Comment: Additional data and analysis in PDF format is available for download at the publications section of our website: http://www.amop.phy.cam.ac.uk/amop-ma

Improving the performance of bright quantum dot single photon sources using amplitude modulation

Single epitaxially-grown semiconductor quantum dots have great potential as single photon sources for photonic quantum technologies, though in practice devices often exhibit non-ideal behavior. Here, we demonstrate that amplitude modulation can improve the performance of quantum-dot-based sources. Starting with a bright source consisting of a single quantum dot in a fiber-coupled microdisk cavity, we use synchronized amplitude modulation to temporally filter the emitted light. We observe that the single photon purity, temporal overlap between successive emission events, and indistinguishability can be greatly improved with this technique. As this method can be applied to any triggered single photon source, independent of geometry and after device fabrication, it is a flexible approach to improve the performance of solid-state systems, which often suffer from excess dephasing and multi-photon background emission

Efficient coupling of photons to a single molecule and the observation of its resonance fluorescence

Single dye molecules at cryogenic temperatures display many spectroscopic phenomena known from free atoms and are thus promising candidates for fundamental quantum optical studies. However, the existing techniques for the detection of single molecules have either sacrificed the information on the coherence of the excited state or have been inefficient. Here we show that these problems can be addressed by focusing the excitation light near to the absorption cross section of a molecule. Our detection scheme allows us to explore resonance fluorescence over 9 orders of magnitude of excitation intensity and to separate its coherent and incoherent parts. In the strong excitation regime, we demonstrate the first observation of the Mollow triplet from a single solid-state emitter. Under weak excitation we report the detection of a single molecule with an incident power as faint as 150 attoWatt, paving the way for studying nonlinear effects with only a few photons.Comment: 6 figure

On-demand semiconductor single-photon source with near-unity indistinguishability

Single photon sources based on semiconductor quantum dots offer distinct advantages for quantum information, including a scalable solid-state platform, ultrabrightness, and interconnectivity with matter qubits. A key prerequisite for their use in optical quantum computing and solid-state networks is a high level of efficiency and indistinguishability. Pulsed resonance fluorescence (RF) has been anticipated as the optimum condition for the deterministic generation of high-quality photons with vanishing effects of dephasing. Here, we generate pulsed RF single photons on demand from a single, microcavity-embedded quantum dot under s-shell excitation with 3-ps laser pulses. The pi-pulse excited RF photons have less than 0.3% background contributions and a vanishing two-photon emission probability. Non-postselective Hong-Ou-Mandel interference between two successively emitted photons is observed with a visibility of 0.97(2), comparable to trapped atoms and ions. Two single photons are further used to implement a high-fidelity quantum controlled-NOT gate.Comment: 11 pages, 11 figure

Full counting statistics of quantum dot resonance fluorescence

The electronic energy levels and optical transitions of a semiconductor quantum dot are subject to dynamics within the solid-state environment. In particular, fluctuating electric fields due to nearby charge traps or other quantum dots shift the transition frequencies via the Stark effect. The environment dynamics are mapped directly onto the fluorescence under resonant excitation and diminish the prospects of quantum dots as sources of indistinguishable photons in optical quantum computing. Here, we present an analysis of resonance fluorescence fluctuations based on photon counting statistics which captures the underlying time-averaged electric field fluctuations of the local environment. The measurement protocol avoids dynamic feedback on the electric environment and the dynamics of the quantum dot's nuclear spin bath by virtue of its resonant nature and by keeping experimental control parameters such as excitation frequency and external fields constant throughout. The method introduced here is experimentally undemanding

Quadrature squeezed photons from a two-level system.

Resonance fluorescence arises from the interaction of an optical field with a two-level system, and has played a fundamental role in the development of quantum optics and its applications. Despite its conceptual simplicity, it entails a wide range of intriguing phenomena, such as the Mollow-triplet emission spectrum, photon antibunching and coherent photon emission. One fundamental aspect of resonance fluorescence--squeezing in the form of reduced quantum fluctuations in the single photon stream from an atom in free space--was predicted more than 30 years ago. However, the requirement to operate in the weak excitation regime, together with the combination of modest oscillator strength of atoms and low collection efficiencies, has continued to necessitate stringent experimental conditions for the observation of squeezing with atoms. Attempts to circumvent these issues had to sacrifice antibunching, owing to either stimulated forward scattering from atomic ensembles or multi-photon transitions inside optical cavities. Here, we use an artificial atom with a large optical dipole enabling 100-fold improvement of the photon detection rate over the natural atom counterpart and reach the necessary conditions for the observation of quadrature squeezing in single resonance-fluorescence photons. By implementing phase-dependent homodyne intensity-correlation detection, we demonstrate that the electric field quadrature variance of resonance fluorescence is three per cent below the fundamental limit set by vacuum fluctuations, while the photon statistics remain antibunched. The presence of squeezing and antibunching simultaneously is a fully non-classical outcome of the wave-particle duality of photons.We acknowledge financial support from the University of Cambridge, the European Research Council ERC Consolidator Grant Agreement No. 617985 and the EU-FP7 Marie Curie Initial Training Network S3NANO. C.M. acknowledges Clare College Cambridge for financial support through a Junior Research Fellowship.This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nature1486

Optical control of one and two hole spins in interacting quantum dots

A single hole spin in a semiconductor quantum dot has emerged as a quantum bit that is potentially superior to an electron spin. A key feature of holes is that they have a greatly reduced hyperfine interaction with nuclear spins, which is one of the biggest difficulties in working with an electron spin. It is now essential to show that holes are viable for quantum information processing by demonstrating fast quantum gates and scalability. To this end we have developed InAs/GaAs quantum dots coupled through coherent tunneling and charged with controlled numbers of holes. We report fast, single qubit gates using a sequence of short laser pulses. We then take the important next step toward scalability of quantum information by optically controlling two interacting hole spins in separate dots.Comment: 5 figure

Photon-Atom Coupling with Parabolic Mirrors

Efficient coupling of light to single atomic systems has gained considerable attention over the past decades. This development is driven by the continuous growth of quantum technologies. The efficient coupling of light and matter is an enabling technology for quantum information processing and quantum communication. And indeed, in recent years much progress has been made in this direction. But applications aside, the interaction of photons and atoms is a fundamental physics problem. There are various possibilities for making this interaction more efficient, among them the apparently 'natural' attempt of mode-matching the light field to the free-space emission pattern of the atomic system of interest. Here we will describe the necessary steps of implementing this mode-matching with the ultimate aim of reaching unit coupling efficiency. We describe the use of deep parabolic mirrors as the central optical element of a free-space coupling scheme, covering the preparation of suitable modes of the field incident onto these mirrors as well as the location of an atom at the mirror's focus. Furthermore, we establish a robust method for determining the efficiency of the photon-atom coupling.Comment: Book chapter in compilation "Engineering the Atom-Photon Interaction" published by Springer in 2015, edited by A. Predojevic and M. W. Mitchell, ISBN 9783319192307, http://www.springer.com/gp/book/9783319192307. Only change to version1: now with hyperlinks to arXiv eprints of other book chapters mentioned in this on

The evaluation of risk for obstructive sleep apnea in patients with type 2 diabetes

Cilj istraživanja je procijeniti rizik za opstrukcijsku apneju tijekom spavanja (engl. Obstructive sleep apnea, OSA) u bolesnika sa šećernom bolešću tipa 2, s pomoću STOP upitnika (engl. Snoring, Tiredness, Observed, Pressure; STOP). S pomoću Epworthove ljestvice pospanosti (ESS) procijenjena je prekomjerna dnevna pospanost i ispitana povezanost pospanosti i rizika za OSA-u u bolesnika sa šećernom bolešću tipa 2. Dosadašnja istraživanja pokazala su da oštećena tolerancije glukoze i šećerna bolest tipa 2 predstavljaju čimbenik rizika za OSA-u, ali i da OSA predstavlja čimbenik rizika za šećernu bolest tipa 2. U našem istraživanju sudjelovala su 252 ispitanika sa šećernom bolešću tipa 2, koji su bili anketirani za vrijeme redovitih pregleda u Kliničkom bolničkom centru Split. Rezultati našeg istraživanja pokazali su da je 156 ispitanika (61,9%) imalo povećan rizik za OSA-u prema rezultatima STOP upitnika. Nadalje, ispitanici koji su imali povećani rizik u odnosu na ispitanike koji nisu imali rizik za OSA-u bili su stariji (65 vs. 61 godina, p < 0,05), imali viši indeks tjelesne mase (28,6 ± 5,1 vs. 26,5 ± 4,1, p < 0,001), veći opseg vrata (41,5 ± 4,7 vs. 39,6 ± 6,2, p < 0,009) i bili pospaniji prema rezultatima ESS (5,3 ± 3,1 vs. 3,9 ± 2,5, p < 0,001). Uz šećernu bolest, većina ispitanika imala je i pridružene bolesti: arterijska hipertenzija (46%), gastroezofagealna refluksna bolest (28%), depresija (10%) i astma (8%). OSA je dio širokoga spektra poremećaja disanja tijekom spavanja koja se dovodi u vezu s metaboličkim poremećajima poput šećerne bolesti tipa 2, a epidemiološki podaci o zastupljenosti OSA u Hrvatskoj su nedostatni. Ovo istraživanje ukazuje na potrebu provođenja probira za OSA u bolesnika sa šećernom bolešću tipa 2, koristeći STOP upitnik.The aim of this study was to evaluate the risk for obstructive sleep apnea (OSA) in patients with type 2 diabetes using the STOP questionnaire (Snoring, Tiredness, Observed, Pressure; STOP). Excessive daytime sleepiness was evaluated with the Epworth sleepiness scale (ESS). Previous studies support the idea that glucose intolerance and type 2 diabetes might represent risk factors for OSA, as well as the idea of OSA being the risk factor for type 2 diabetes. A total of 252 patients with type 2 diabetes were surveyed during the regular follow-up in the Regional Centre for Diabetes, Endocrinology and Metabolic Diseases of Split University Hospital. The results of our study indicate that 156 patients (61.9%) had increased risk for OSA according to STOP questionnaire score. In addition, those at high risk for OSA were older (65 vs. 61 years of age, p < 0.05), had higher body mass index (BMI, 28.6 ± 5.1 vs. 26.5 ± 4.1, p < 0.001), higher neck circumference (41.5 ± 4.7 vs. 39.6 ± 6.2, p < 0.009), and had excessive daytime sleepiness according to the ESS score (5.3 ± 3.1 vs. 3.9 ± 2.5, p < 0.001). Individuals with type 2 diabetes reported to have comorbidities, mainly hypertension (46%), gastroesophageal reflux disease (28%), depression (10%), and asthma (8%). Based on current evidence from literature, OSA could be related to clinical conditions such as diabetes and essential hypertension. More epidemiological data are needed to establish the prevalence of OSA in Croatian patients with type 2 diabetes. Our findings indicate the relevance of STOP questionnaire use as a screening tool for obstructive sleep apnea in patients with type 2 diabetes in Croatia