Manipulating light on a chip for quantum technologies
(糖心视频Org.com) -- A team of physicists and engineers at Bristol University has demonstrated exquisite control of single particles of light 鈥� photons 鈥� on a silicon chip to make a major advance towards long-sought-after quantum technologies, including super-powerful quantum computers and ultra-precise measurements.
The Bristol Centre for Quantum Photonics has demonstrated precise control of four photons using a microscopic metal electrode lithographically patterned onto a silicon chip.
The photons propagate in silica waveguides 鈥� much like in optical fibres 鈥� patterned on a silicon chip, and are manipulated with the electrode, resulting in a high-performance miniaturized device.
鈥淲e have been able to generate and manipulate entangled states of photons on a silicon chip鈥� said PhD student, Jonathan Matthews, who together with Alberto Politi performed the experiments. 鈥淭hese entangled states are responsible for famously 鈥榳eird鈥� behaviour arising in quantum mechanics, but are also at the heart of powerful quantum technologies.鈥�
鈥淭his precise manipulation is a very exciting development for fundamental science as well as for future quantum technologies.鈥� said Prof Jeremy O鈥橞rien, Director of the Centre for Quantum Photonics, who led the research.
The team reports its results in the latest issue of , a sister journal of the leading science journal Nature, and in a Postdeadline Paper at 'The International Quantum Electronics Conference (IQEC)' on June 4 in Baltimore, USA [IQEC Postdeadline Papers].
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 microscopic scales.
For example a quantum computer relies on the fact that quantum particles, such as photons, can exist in a 鈥渟uperposition鈥� of two states at the same time 鈥� in stark contrast to the transistors in a PC which can only be in the state 鈥�0鈥� or 鈥�1鈥�.
Photons are an excellent choice for quantum technologies because they are relatively noise-free; information can be moved around at the speed of light; and manipulating single photons is easy.
Making two photons 鈥渢alk鈥� to each other to generate the all-important entangled states is much harder, but Professor O鈥橞rien and his colleagues at the University of Queensland demonstrated this in a quantum logic gate back in 2003 [Nature 426, 264 (2003)].
Last year, the Centre for Quantum Photonics at Bristol showed how such interactions between photons could be realised on a silicon chip, pointing the way to advanced quantum technologies based on photons [].
Photons are also required to 鈥渢alk鈥� to each other to realise the ultra-precise measurements that harness the laws of quantum mechanics. In 2007 Professor O鈥橞rien and his Japanese collaborators reported such a quantum metrology measurement with four photons [].
Manipulating photons on a silicon chip
鈥淒espite these impressive advances, the ability to manipulate photons on a chip has been missing,鈥� said Mr Politi. 鈥淔or the last several years the Centre for Quantum Photonics has been working towards building fully functional quantum circuits on a chip to solve these problems,鈥� added Prof O鈥橞rien.
The team coupled photons into and out of the chip, fabricated at CIP Technologies, using optical fibres. Application of a voltage across the metal electrode changed the temperature of the silica waveguide directly beneath it, thereby changing the path that the photons travelled. By measuring the output of the device they confirmed high-performance manipulation of photons in the chip.
The researchers proved that one of the strangest phenomena of the quantum world, namely 鈥渜uantum entanglement鈥�, was achieved on-chip with up to four photons. Quantum entanglement of two particles means that the state of either of the particles is not defined, but only their collective state, and results in an instantaneous linking of the particles.
This on-chip entanglement has important applications in quantum metrology and the team demonstrated an ultra-precise measurement in this way.
鈥淎s 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,鈥� said Alberto Politi.
鈥淭he really exciting thing about this result is that it will enable the development of reconfigurable and adaptive quantum circuits for photons. This opens up all kinds of possibilities,鈥� said Prof O鈥橞rien.
A commentary on the work that appeared in the same issue [] described it as 鈥渁n important step in the quest for quantum computation鈥� and concluded: 鈥淭he most exciting thing about this work is its potential for scalability. The small size of the [device] means that far greater complexity is possible than with large-scale optics.鈥�
The other co-author of the Nature Photonics paper is Dr Andr茅 Stefanov, formerly a Research fellow in the Centre for Quantum Photonics, and now at the Federal Office of Metrology METAS, Switzerland.
Provided by University of Bristol ( : )
