Multi-Purpose Photonic Chip Paves the Way to Programmable Quantum Processors

A multi-purpose optical chip which generates, manipulates and
measures entanglement and mixture -- two
quantum phenomena which are essential driving
forces for tomorrow's quantum computers -- has
been developed by researchers from the
University of Bristol's Centre for Quantum Photonics. This work represents an important
step forward in the race to develop a quantum
computer. The fundamental resource
that drives a quantum
computer is entanglement
-- the connection between
two distant particles which
Einstein famously called 'spooky action at a
distance'. The Bristol
researchers have, for the
first time, shown that this
remarkable phenomenon
can be generated, manipulated and measured
entirely on a tiny silica chip.
They have also used the
same chip to measure
mixture -- an often
unwanted effect from the environment, but a
phenomenon which can
now be controlled and
used to characterize
quantum circuits, as well as being of fundamental interest to physicists. "In order to build a quantum computer, we not
only need to be able to control complex
phenomena such as entanglement and mixture,
but we need to be able to do this on a chip, so
that we can scalably and practically duplicate
many such miniature circuits -- in much the same way as the modern computers we have today,"
says Professor Jeremy O'Brien, Director of the
Centre for Quantum Photonics. "Our device
enables this and we believe it is a major step
forward towards optical quantum computing." The chip, which performs several experiments
that would each ordinarily be carried out on an
optical bench the size of a large dining table, is 70
mm by 3 mm. It consists of a network of tiny
channels which guide, manipulate and interact
single photons -- particles of light. Using eight reconfigurable electrodes embedded in the
circuit, photon pairs can be manipulated and
entangled, producing any possible entangled
state of two photons or any mixed state of one
photon. "It isn't ideal if your quantum computer can only
perform a single specific task," explains Peter
Shadbolt, lead author of the study, which is
published in the journal Nature Photonics. "We
would prefer to have a reconfigurable device
which can perform a broad variety of tasks, much like our desktop PCs today -- this
reconfigurable ability is what we have now
demonstrated. This device is approximately ten
times more complex than previous experiments
using this technology. It's exciting because we
can perform many different experiments in a very straightforward way, using a single
reconfigurable chip." The researchers, who have been developing
quantum photonic chips for the past six years,
are now working on scaling up the complexity
of this device, and see this technology as the
building block for the quantum computers of the
future. Dr Terry Rudolph from Imperial College in London,
UK, believes this work is a significant advance. He
said: "Being able to generate, manipulate and
measure entanglement on a chip is an awesome
achievement. Not only is it a key step towards
the many quantum technologies -- such as optical quantum computing -- which are going to
revolutionize our lives, it gives us much more
opportunity to explore and play with some of the
very weird quantum phenomena we still
struggle to wrap our minds around. They have
made it so easy to dial up in seconds an experiment that used to take us months, that I'm
wondering if even I can run my own experiment
now!"