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Jean-François Roch

Publications and source records attributed to Jean-François Roch.

30 records · Page 2Linked to original sources
arXiv2013

Magnetometry with nitrogen-vacancy ensembles in diamond based on infrared absorption in a doubly resonant optical cavity

We propose to use an optical cavity to enhance the sensitivity of magnetometers relying on the detection of the spin state of high-density nitrogen-vacancy ensembles in diamond using infrared optical absorption. The role of the cavity is to obtain a contrast in the absorption-detected magnetic resonance approaching unity at room temperature. We project an increase in the photon shot-noise limited sensitivity of two orders of magnitude in comparison with a single-pass approach. Optical losses can limit the enhancement to one order of magnitude which could still enable room temperature operation. Finally, the optical cavity also allows to use smaller pumping power when it is designed to be resonant at both the pump and the signal wavelength.

physics.optics↗
arXiv2012

Free induction decay of single spins in diamond

We study both theoretically and experimentally the free induction decay (FID) of the electron spin associated with a single nitrogen-vacancy defect in high purity diamond, where the main source of decoherence is the hyperfine interaction with a bath of $^{13}$C nuclear spins. In particular, we report a systematic study of the FID signal as a function of the strength of a magnetic field oriented along the symmetry axis of the defect. On average, an increment of the coherence time by a factor of $\sqrt{5/2}$ is observed at high magnetic field in diamond samples with a natural abundance of $^{13}$C nuclear spins, in agreement with numerical simulations and theoretical studies. Further theoretical analysis shows that this enhancement is independent of the concentration of nuclear spin impurities. By dividing the nuclear spin bath into shells and cones, we theoretically identify which nuclear spins are responsible for the observed dynamics.

cond-mat.mes-hall↗
arXiv2010

Controlling single diamond NV color center photoluminescence spectrum with a Fabry-Perot microcavity

We present both theoretical and experimental results on fluorescence of single defect centers in diamond nanocrystals embedded in a planar dielectric microcavity. From a theoretical point of view, we show that the overall fluorescence collection efficiency using moderate numerical aperture microscope objective can be enhanced by using a low quality factor microcavity. This could be used in particular for low temperature applications where the numerical aperture of collection microscope objectives is limited due to the experimental constraints. We experimentally investigate the control of the fluorescence spectrum of the emitted light from a single center. We show the simultaneous narrowing of the room temperature broadband emission spectrum and the increase of the fluorescence spectral density.

physics.optics↗
arXiv2010

Optical determination and magnetic manipulation of single nitrogen-vacancy color center in diamond nanocrystal

The controlled and coherent manipulation of individual quantum systems is a fundamental key for the development of quantum information processing. The nitrogen-vacancy (NV) color center in diamond is a promising system since its photoluminescence is perfectly stable at room temperature and its electron spin can be optically read-out at the individual level. We review here the experiments currently realized in our laboratory, concerning the use of single NV color center as single photon source and the coherent magnetic manipulation of the electron spin associated to a single NV color center. Furthermore, we demonstrate a nanoscopy experiment based on saturation absorption effect, which allows to optically pin-point single NV color center at a sub-? resolution. This opens a possibility to independently address two or multiple magnetically-coupled single NV color centers, which is a necessary step toward the realization of a diamond-based quantum computer.

physics.optics↗
arXiv2009

Influence of a static magnetic field on the photoluminescence of an ensemble of Nitrogen-Vacancy color centers in a diamond single-crystal

We investigate the electron spin resonance of an ensemble of Nitrogen-Vacancy (NV) color centers in a bulk diamond crystal. The four possible orientations of the NV-center in the lattice lead to different dependences on the magnitude and the orientation of an external static magnetic field. Experimental results obtained with a continuous microwave excitation are in good agreement with simulations. In addition, we observe that the average radiative lifetime of the NV color center is also modified when the external magnetic field is applied. This variation is explained by the mixing between mS = 0 and mS = $\pm$1 spin states of the NV-center with different radiative lifetimes, due to magnetic coupling. These results are of interest for a broad range of applications, such as spin-resonance-based magnetometry with a high-density ensemble of NV-centers

cond-mat.mtrl-sci↗
arXiv2008

Delayed-choice test of complementarity with single photons

We report an experimental test of complementarity using clock-triggered single-photon pulses emitted by an individual N-V color center in a diamond nanocrystal. The single photons are sent into a Mach-Zehnder interferometer with an output beamsplitter of adjustable reflection coefficient R. In addition, the choice of introducing or removing this beamsplitter is random and relativistically space-like separated from the entering of the photon inside the interferometer, as required for the Wheeler's delayed-choice regime. Each set value of R allows us to observe interference with visibility V and to obtain incomplete which-path information characterized by the distinguishability D. The measured values of V and D are found to obey the complementarity relation V^2 + D^2 =< 1.

quant-ph↗
arXiv2007

Room temperature triggered single-photon source in the near infrared

We report the realization of a solid-state triggered single-photon source with narrow emission in the near infrared at room temperature. It is based on the photoluminescence of a single nickel-nitrogen NE8 colour centre in a chemical vapour deposited diamond nanocrystal. Stable single-photon emission has been observed in the photoluminescence under both continuous-wave and pulsed excitations. The realization of this source represents a step forward in the application of diamond-based single-photon sources to Quantum Key Distribution (QKD) under practical operating conditions.

quant-ph↗
arXiv2007

Enhancing single-molecule photostability by optical feedback from quantum-jump detection

We report an optical technique that yields an enhancement of single-molecule photostability, by greatly suppressing photobleaching pathways which involve photoexcitation from the triplet state. This is accomplished by dynamically switching off the excitation laser when a quantum-jump of the molecule to the triplet state is optically detected. This procedure leads to a lengthened single-molecule observation time and an increased total number of detected photons. The resulting improvement in photostability unambiguously confirms the importance of photoexcitation from the triplet state in photobleaching dynamics, and may allow the investigation of new phenomena at the single-molecule level.

quant-ph↗
arXiv2006

Experimental realization of Wheeler's delayed-choice GedankenExperiment

The quantum "mystery which cannot go away" (in Feynman's words) of wave-particle duality is illustrated in a striking way by Wheeler's delayed-choice GedankenExperiment. In this experiment, the configuration of a two-path interferometer is chosen after a single-photon pulse has entered it : either the interferometer is \textit{closed} (\textit{i.e.} the two paths are recombined) and the interference is observed, or the interferometer remains \textit{open} and the path followed by the photon is measured. We report an almost ideal realization of that GedankenExperiment, where the light pulses are true single photons, allowing unambiguous which-way measurements, and the interferometer, which has two spatially separated paths, produces high visibility interference. The choice between measuring either the 'open' or 'closed' configuration is made by a quantum random number generator, and is space-like separated -- in the relativistic sense -- from the entering of the photon into the interferometer. Measurements in the closed configuration show interference with a visibility of 94%, while measurements in the open configuration allow us to determine the followed path with an error probability lower than 1%.

quant-ph↗
arXiv2006

Balanced homodyne detection in second-harmonic generation microscopy

We demonstrate the association of two-photon nonlinear microscopy with balanced homodyne detection for investigating second harmonic radiation properties at nanoscale dimensions. Variation of the relative phase between second-harmonic and fundamental beams is retrieved, as a function of the absolute orientation of the nonlinear emitters. Sensitivity down to approximately 3.2 photon/s in the spatio-temporal mode of the local oscillator is obtained. This value is high enough to efficiently detect the coherent second-harmonic emission from a single KTiOPO4 crystal of sub-wavelength size.

physics.optics↗
arXiv2005

Narrow-band single-photon emission in the near infrared for quantum key distribution

We report on the observation of single colour centers in natural diamond samples emitting in the near infrared region when optically excited. Photoluminescence of these single emitters have several striking features, such as a narrow-band fully polarized emission (FWHM 2 nm) around 780 nm, a short excited-state lifetime of about 2 ns, and perfect photostability at room temperature under our excitation conditions. We present a detailed study of their photophysical properties. Development of a triggered single-photon source relying on this single colour centre is discussed in the prospect of its application to quantum key distribution.

quant-ph↗