News and New Products

Semiconductor Used to Generate Entangled Photons

By Harry Yeates -- Electronics Weekly, 1/17/2006

A simple means of generating pairs of photons that can be used for quantum computation, quantum cryptographic key distribution and for ultra-fine lithography has been developed by researchers at Toshiba’s Cambridge, U.K., labs.

It is the first time so-called “entangled” photon pairs have been produced on demand from a semiconductor quantum dot and, although certain engineering issues still need to be addressed, commercial devices could be available in three years time.

“What’s very interesting about this source is that we can trigger the generation of the entangled photons on demand,” said Dr. Andrew Shields, who leads the research group. “That’s very important for some applications such as quantum computing, where you may have a clock and want to synchronize all of the gate operations to that clock.”
      
The most common technique for creating entangled photons – in which the state of one is intimately tied to and affected by that of the other – is a method known as parametric down-conversion, in which a lithium niobate crystal is pumped by a powerful laser. This is a non-linear process with no control over the generation time or the number of pairs produced.

The Toshiba device works by subjecting a quantum dot of InAs/GaAs to a laser pulse. Depending on the dot’s shape, or the local magnetic field, entangled photo pairs can be generated controllably.

The process is currently carried out at around 10K, but Shields said raising that to temperature to the point where closed-cycle or thermo-electric coolers could be used was entirely possible.

“What’s also interesting is we are generating our entangled pairs from a simple semiconductor device, so we can make it more compact and robust, and potentially it can be manufactured cheaply,” said Shields.

Electronics Weekly is the London-based sister publication of Electronic News.