Scientists at Toshiba's European research headquarters have
developed a novel single-photon detector based on quantum dots that
could dramatically improve the performance of quantum cryptographic
communications.
"One of the reasons we're very excited about this work is that
it could increase the bit rate in a quantum cryptographic system,"
said Dr Andrew Shields, leader of the quantum information group at
Toshiba Research Europe in Cambridge.
The device detects the loss or capture of a single charge in a
quantum dot by sensing a change in the resonant tunnelling current
through a double barrier structure. The detector operates with a
detection efficiency of 12.5 per cent, with a time resolution of
150ns.
However, what makes it particularly suitable for quantum
cryptography is its inherently low noise. Existing systems,
including Toshiba's own, use avalanche photodiodes, which limit the
maximum bit rate as a result of afterpulses, which are manifested
as spurious detection events.
Using the new detector might mean that the limit to higher bit
rates becomes the speed of the detector. Shields said the 150ns
resolution achieved so far is due to the capacitance of the
packaging, and could theoretically be reduced to less than a
nanosecond.
"Gigahertz clock rates would mean we could increase the bit
rates by two orders of magnitude," said Shields, "and that would be
a fantastic advance."
The current device is built in a GaAs process. Shields said the
next step is to make a similar structure in indium phosphide,
operating in the infra red. The work appeared in the journal
Physical Review Letters.
www.toshiba-europe.com/research/crl