Quantum jump photodetector for narrowband photon counting with a single atom

Using a single neutral <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mmultiscripts><a:mi>Rb</a:mi><a:mprescripts/><a:none/><a:mrow><a:mn>87</a:mn></a:mrow></a:mmultiscripts></a:mrow></a:math> atom held in an optical trap, and “quantum jump” detection of single-photon-initiated state changes, we demonstrate a single-photon quantum jump photodetector (QJPD) with intrinsically narrow bandwidth and strong rejection of out-of-band photons, of interest for detecting weak optical signals in the presence of a strong broadband background. By analyzing fluorescence photon count distributions for the bright and dark states with and without excitation, we measure quantum efficiency of <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:mn>2.9</b:mn><b:mrow><b:mo>(</b:mo><b:mn>2</b:mn><b:mo>)</b:mo></b:mrow><b:mo>×</b:mo><b:msup><b:mn>10</b:mn><b:mrow><b:mo>−</b:mo><b:mn>3</b:mn></b:mrow></b:msup></b:mrow></b:math>, a record for single-pass quantum jump production, and signal-photon-unprovoked “dark jump” rate—analogous to the dark count rate of other detectors —of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mn>3</c:mn><c:mrow><c:mo>(</c:mo><c:mn>10</c:mn><c:mo>)</c:mo></c:mrow><c:mo>×</c:mo><c:msup><c:mn>10</c:mn><c:mrow><c:mo>−</c:mo><c:mn>3</c:mn></c:mrow></c:msup><c:mspace width="0.16em"/><c:mrow><c:mi>jumps</c:mi><c:mo>/</c:mo><c:mi mathvariant="normal">s</c:mi></c:mrow></c:mrow></c:math> during passive accumulation plus <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mrow><f:mn>4.0</f:mn><f:mrow><f:mo>(</f:mo><f:mn>4</f:mn><f:mo>)</f:mo></f:mrow><f:mo>×</f:mo><f:msup><f:mn>10</f:mn><f:mrow><f:mo>−</f:mo><f:mn>3</f:mn></f:mrow></f:msup></f:mrow></f:math> jumps per readout, orders of magnitude below those of traditional single-photon detectors. Available methods can substantially improve QJPD quantum efficiency, dark jump rate, bandwidth, and tunability.