Triggered Source of Single Photons based on Controlled Single Molecule FluorescenceBrunel, et al., Phys. Rev. Lett. 83 (14), 2722 (1999).Norm MoultonLPS15 October, 1999

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OutlineBrief summaryPrevious work leading to this paperAspects of this paperExperimental configurationResults

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Highlights of the paper:Single molecules frozen in a matrixRF electromagnetic field modulates the frequency of a transition in the presence of a laser tuned close to the central fluorescence wavelength.When the resonance is crossed, molecules are pumped into the upper state by dissipated Rabi flopping.

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Highlights, continued:When RF drives resonance wavelength away from laser wavelength, a burst of fluorescence photons is detected.Hanbury-Brown Twiss type experiment reveals clear photon anti-bunching, indicating that single photons are being produced by this process.

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Chaotic (Thermal) LightThermal probability distribution, thermal noise.

Two photon detection correlation drops after t=0.

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Coherent LightPoisson Noise:

Equal two-photon detection correlation:Vacuum quantum noise

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Non-Classical LightExtremely low noise (sub-Poissonian, can be below vacuum)Two-photon time correlation increases from t=0 value.

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Photon Anti-Bunching

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Previous Work With Isolated MoleculesPhys Rev Lett 69 (10), 1516-1519 (1992)

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Spectra of Matrix-Isolated MoleculesOptical traps can isolate and cool atoms, but internal degrees of freedom have made it impossible to trap molecules.Isolating molecules in a host matrix and freezing out degrees of freedom provides a way to study spectra of individual molecules without recoil (zero-phonon transitions).

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Photon Counting with Matrix-Isolated MoleculesTwo photon correlation experiments with single molecules showed clear signatures of anti-bunching and Rabi flopping.S0S1T1Vibronic TransitionFast vibrational transitionElectronic Transition

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Previous Work With RF Phys Rev Lett 81 (13), 2679-2682 (1998)

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Rabi Resonances in RF/Laser FieldsAt high laser power, the states are dressed by the laser and probed by the RF, and vice versa.Frequency splitting between dressed states is the generalized Rabi frequency, Rabi transitionsRabi resonances occur when RF connects the dressed states at high laser power.

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Dressed State PictureAt crossing pt:Dressing field removes the degeneracy:(at crossing point)

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Weak RF CaseSingle molecule line and two Rabi sidebands observed.Sideband splitting decreases as Rabi frequency is increased.

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Strong RF CaseResonances involving several RF photons appear.Spectra are in excellent agreement with predictions of optical Bloch equations.

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Rabi Flopping &Adiabatic FollowingWhen a two level atom or molecule is suddenly exposed to an intense on-resonance field, Rabi flopping occurs.-DNt

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Dissipation of Rabi Flopping by Decohering EffectsRabi flopping dissipates in a few cycles due to finite T1 and T2.The system is left in an indeterminate steady state, withwhere S, the saturation factor, is >>1. There is nearly equal probability of a molecule being in either state.

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Resonance Fluorescence with Pulsed Laser SourceWith system prepared in ground state, apply a Rabi p-Pulse--puts the system into the excited state.Some time after the end of the pulse, the system will return to ground state emitting a photon through fluorescence.

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Photon Emission

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Difficulties Associated with Rabi p-Pulse State InversionRequires precise control of pulse width-very sensitive to fluctuations.Requires precise control of pulse intensity since W depends on the field intensity.

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Another Way: Adiabatic FollowingExpose the system to the resonant field for a time long enough to achieve the steady state value of DN. Remove the resonant field, fluorescence will then occur naturally. Not sensitive to fluctuations in intensity or pulse width since the system is in the flat part of the DN curve.

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Resonance TuningMost experiments use a tunable pulsed laser to interact with an atom with a fixed resonance level.Instead, this work used a fixed wavelength CW laser and tuned the resonance by dynamic Stark effect.Sample was placed between metal electrodes on a glass slide and an RF field on the order of 1 MHz was applied.

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Resonance TuningAs the resonance was tuned past the wavelength of the laser, adiabatic following put about half of the exposed molecules into the upper state.As the molecules were tuned past resonance, the molecules in the excited state emitted photons by fluorescence.A burst of photons was detected each time this occurred.

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-DNtResonance PassagetwRFT1>Tpass > TR; WR >> G

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Experimental TechniqueIncident LaserSampleElectrodesFluorescenceParabolic ReflectorFocusing LensRF Signal Source

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Experimental ParameterswRF=3 MHzWR=2.6G=52 MHzD0=1.6 GHzG=20 MHzPhoton detection rate=6300 counts/s

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ResultsTime constant=8 ns

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Results