Dr Jeremy O’Brien, his PhD student Alberto Politi, and their colleagues at Bristol University have demonstrated the world’s smallest optical controlled-NOT gate – the building block of a quantum computer.
The team were able to fabricate their controlled-NOT gate from silica wave-guides on a silicon chip, resulting in a miniaturised device and high-performance operation.
“This is a crucial step towards a future optical quantum computer, as well as other quantum technologies based on photons,” said Dr O’Brien.
The team reports its results in the March 27 2008 Science Express – the advanced online publication of the journal Science.
Quantum technologies with photons
Quantum technologies aim to exploit the unique properties of quantum mechanics, the physics theory that explains how the world works at very small scales.
For example a quantum computer relies on the fact that quantum particles, such as photons, can exist in a “superposition” of two states at the same time – in stark contrast to the transistors in a PC which can only be in the state “0” or “1”.
Photons are an excellent choice for quantum technologies because they are relatively noise free; information can be moved around quickly – at the speed of light; and manipulating single photons is easy.
Making two photons “talk” to each other to realise the all-important controlled-NOT gate is much harder, but Dr O’Brien and his colleagues at the University of Queensland demonstrated this back in 2003 [Nature 426, 264].
Photons must also “talk” to each other to realise the ultra-precise measurements that harness the laws of quantum mechanics – quantum metrology.
Last year Dr O’Brien and his collaborator Professor Takeuchi and co-workers at Hokkaido University reported such a quantum metrology measurement with four photons [Science 316, 726].
Silica-on-silicon wave-guide quantum circuits
“Despite these and other impressive demonstrations, quantum optical circuits have typically relied on large optical elements with photons propagating in air, and consuming a square metre of optical table. This has made them hard to build and difficult to scale up,” said Alberto Politi.
“For the last several years the Centre for Quantum Photonics has been working towards building controlled-NOT gates and other important quantum circuits on a chip to solve these problems,” added Dr O’Brien.
The team’s chips, fabricated at CIP Technologies, have dimensions measured in millimetres.
This impressive miniaturisation was permitted thanks to the silica-on-silicon technology used in commercial devices for modern optical telecommunications, which guides light on a chip in the same way as in optical fibres.
The team generated pairs of photons which each encoded a quantum bit or qubit of information. They coupled these photons into and out of the controlled-NOT chip using optical fibres. By measuring the output of the device they confirmed high-fidelity operation.
In the experimental characterisation of the quantum chips the researchers also proved that one of the strangest phenomena of the quantum world, namely “quantum entanglement”, was achieved on-chip. Quantum entanglement of two particles means that the state of either of the particles is not defined, but only their collective state.
This on-chip entanglement has important applications in quantum metrology.
“As well as quantum computing and quantum metrology, on-chip photonic quantum circuits could have important applications in quantum communication, since they can be easily integrated with optical fibres to send photons between remote locations,” said Alberto Politi.
Joanne Fryer | EurekAlert!
Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore
Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
05.12.2016 | Power and Electrical Engineering
05.12.2016 | Materials Sciences
05.12.2016 | Power and Electrical Engineering