Norm Moulton LPS 15 October, 1999 “Triggered Source of Single Photons based on Controlled Single Molecule Fluorescence Brunel, et al., Phys. Rev. Lett. 83 (14), 2722 (1999). Norm Moulton LPS 15 October, 1999

Outline Brief summary Previous work leading to this paper Aspects of this paper Experimental configuration Results

Highlights of the paper: Single molecules frozen in a matrix RF 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.

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.

Chaotic (Thermal) Light Thermal probability distribution, thermal noise. Two photon detection correlation drops after t=0.

Coherent Light Poisson Noise: Equal two-photon detection correlation: Vacuum quantum noise

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

Photon Anti-Bunching

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

Spectra of Matrix-Isolated Molecules Optical 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).

Photon Counting with Matrix-Isolated Molecules Two photon correlation experiments with single molecules showed clear signatures of anti-bunching and Rabi flopping. Vibronic Transition S1 T1 Electronic Transition Fast vibrational transition S0

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

Rabi Resonances in RF/Laser Fields At 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 transitions” Rabi resonances occur when RF connects the dressed states at high laser power.

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

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

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

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

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

-DN t

Resonance Fluorescence with Pulsed Laser Source With 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.

p-Pulse t -DN Ilaser Photon Emission

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

Another Way: Adiabatic Following Expose 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.

Resonance Tuning Most 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.

Resonance Tuning As 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.

T1>Tpass > TR; WR >> G -DN t wRF t Resonance Passage T1>Tpass > TR; WR >> G

Experimental Technique Parabolic Reflector Fluorescence Electrodes Sample Incident Laser Focusing Lens RF Signal Source

Experimental Parameters wRF=3 MHz WR=2.6G=52 MHz D0=1.6 GHz G=20 MHz Photon detection rate=6300 counts/s

Results Time constant=8 ns

Results