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D e t e r m i n i s t i c S i n g l e P h o t o n s |
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Deterministic single photon experimental setup. |
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We have proposed a deterministic single-photon source based on an ensemble of atomic emitters, measurement, and
conditional quantum evolution. We reported the implementation
of this scheme using a cold rubidium vapor, with a
measured efficiency of 1%–2%. In common with the
cavity QED system, our source is suitable for reversible
quantum state transfer between atoms and light, a prerequisite
for a quantum network. The source is stationary
and produces a photoelectric detection record with truly
sub-Poissonian statistics.
The key idea of our protocol is that a single photon can
be generated at a predetermined time if we know that the
medium contains an atomic excitation. The presence of the
latter is heralded by the measurement of a scattered photon
in a write process. Since this is intrinsically probabilistic, it
is necessary to perform independent, sequential write trials
before the excitation is heralded. After this point one
simply waits and reads out the excitation at the predetermined
time. The performance of repeated trials and heralding
measurements represents a conditional feedback
process and the duration of the protocol is limited by the
coherence time of the atomic excitation. Our system has
therefore two crucial elements: (a) a high-quality probabilistic
source of heralded photons and (b) long atomic
coherence times. With constant improvement in readout efficiencies and quantum memory times, we are perfecting this deterministic single photon source with an eye towards linear optics quantum computation.
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The above photo features an ultra-cold cloud (~100uK) of 109 neutral rubidium-85 atoms suspended in ultra high vacuum via a magneto-optical trap. This sample of atoms is used for deterministic generation of single photons. |
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