19 research outputs found
High resolution coherent population trapping on a single hole spin in a semiconductor
We report high resolution coherent population trapping on a single hole spin
in a semiconductor quantum dot. The absorption dip signifying the formation of
a dark state exhibits an atomic physics-like dip width of just 10 MHz. We
observe fluctuations in the absolute frequency of the absorption dip, evidence
of very slow spin dephasing. We identify this process as charge noise by,
first, demonstrating that the hole spin g-factor in this configuration
(in-plane magnetic field) is strongly dependent on the vertical electric field,
and second, by characterizing the charge noise through its effects on the
optical transition frequency. An important conclusion is that charge noise is
an important hole spin dephasing process
Single-emitter quantum key distribution over 175 km of fiber with optimised finite key rates
Quantum key distribution with solid-state single-photon emitters is gaining
traction due to their rapidly improving performance and compatibility with
future quantum network architectures. In this work, we perform fibre-based
quantum key distribution with a quantum dot frequency-converted to telecom
wavelength, achieving count rates of 1.6 MHz with
. We demonstrate positive key rates
up to 175 km in the asymptotic regime. We then show that the community standard
analysis for non-decoy state QKD drastically overestimates the acquisition time
required to generate secure finite keys. Our improved analysis using the
multiplicative Chernoff bound reduces the required number of received signals
by a factor of over existing work, with the finite key rate approaching
the asymptotic limit at all achievable distances for acquisition times of one
hour. Over a practical distance of 100 km we achieve a finite key rate of 13
kbps after one minute of integration time. This result represents major
progress towards the feasibility of long-distance single-emitter QKD networks.Comment: 9 pages, 3 figure
Single-emitter quantum key distribution over 175 km of fibre with optimised finite key rates
Quantum key distribution with solid-state single-photon emitters is gaining traction due to their rapidly improving performance and compatibility with future quantum networks. Here we emulate a quantum key distribution scheme with quantum-dot-generated single photons frequency-converted to 1550 nm, achieving count rates of 1.6 MHz with g20=3.6% and asymptotic positive key rates over 175 km of telecom fibre. We show that the commonly used finite-key analysis for non-decoy state QKD drastically overestimates secure key acquisition times due to overly loose bounds on statistical fluctuations. Using the tighter multiplicative Chernoff bound to constrain the estimated finite key parameters, we reduce the required number of received signals by a factor 108. The resulting finite key rate approaches the asymptotic limit at all achievable distances in acquisition times of one hour, and at 100 km we generate finite keys at 13 kbps for one minute of acquisition. This result is an important step towards long-distance single-emitter quantum networking
A tunable microcavity
We present a generic microcavity platform for cavity experiments on optically active nanostructures, such as quantum dots, nanocrystals, color centers, and carbon nanotubes. The cavity is of the Fabry-Perot type with a planar back mirror and a miniature concave top mirror with radius of curvature similar to 100 mu m. Optical access is achieved by free beam coupling, allowing good mode-matching to the cavity mode. The cavity has a high Q-factor, reasonably small mode volume, open access, spatial and spectral tunability, and operates at cryogenic temperatures. Spectral and spatial tuning of the Purcell effect (weak coupling regime) on a single InGaAs quantum dot is demonstrated. (C) 2011 American Institute of Physics. [doi:10.1063/1.3632057
High Resolution Coherent Population Trapping on a Single Hole Spin in a Semiconductor Quantum Dot
A bright source of telecom single photons based on quantum frequency conversion
On-demand indistinguishable single photon sources are essential for quantum
networking and communication. Semiconductor quantum dots are among the most
promising candidates, but their typical emission wavelength renders them
unsuitable for use in fibre networks. Here, we present quantum frequency
conversion of near-infrared photons from a bright quantum dot to the
telecommunication C-band, allowing integration with existing fibre
architectures. We use a custom-built, tunable 2400 nm seed laser to convert
single photons from 942 nm to 1550 nm in a difference frequency generation
process. We achieve an end-to-end conversion efficiency of 35%,
demonstrate count rates approaching 1 MHz at 1550 nm with
, and achieve Hong-Ou-Mandel
visibilities of 60%. We expect this scheme to be preferable to quantum dot
sources directly emitting at telecom wavelengths for fibre based quantum
networking.Comment: 7 pages, 4 figure