Tiny photonics logic circuit achieves quantum entanglement
March 28, 2008
A team of physicists and engineers has demonstrated exquisite control of single particles of light—photons—on a silicon chip to make a major advance towards the long sought after goal of a super-powerful quantum computer.
Jeremy O’Brien, his Ph.D. student Alberto Politi, and their colleagues at Bristol Univ. have demonstrated the world’s smallest optical controlled-NOT gate—the building block of a quantum computer.
The team was able to fabricate their controlled-NOT gate from silica wave-guides on a silicon chip, resulting in a miniaturized 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,” says O’Brien.
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 realize the all-important controlled-NOT gate is much harder, but O’Brien and his colleagues at the Univ. of Queensland, Australia, demonstrated this back in 2003.
Photons must also “talk” to each other to realize the ultra-precise measurements that harness the laws of quantum mechanics—quantum metrology.
Last year, O’Brien and his collaborator Professor Takeuchi and co-workers at Hokkaido Univ. reported such a quantum metrology measurement with four photons.
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 meter of optical table. This has made them hard to build and difficult to scale up,” says 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,” adds O’Brien.
The team’s chips, fabricated at CIP Technologies, have dimensions measured in millimeters.
This impressive miniaturization 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 fibers.
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 fibers. By measuring the output of the device they confirmed high-fidelity operation.
In the experimental characterization 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.
The team reported its results in the March 27 Science Express. In addition to O’Brien and Alberto Politi co-authors of the Science paper are Martin Cryan, Professor John Rarity, and Siyuan Yu.
The work was funded by the U.S. government Intelligence Advanced Research Projects Activity (IARPA), the Quantum Information Processing Interdisciplinary Research Collaboration (QIP IRC), the Engineering and Physical Sciences Research Council (EPSRC), and the Leverhulme Trust.
SOURCE: Univ. of Bristol, UK
A team of physicists and engineers has demonstrated exquisite control of single particles of light—photons—on a silicon chip to make a major advance towards the long sought after goal of a super-powerful quantum computer.
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The team was able to fabricate their controlled-NOT gate from silica wave-guides on a silicon chip, resulting in a miniaturized 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,” says O’Brien.
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 realize the all-important controlled-NOT gate is much harder, but O’Brien and his colleagues at the Univ. of Queensland, Australia, demonstrated this back in 2003.
Photons must also “talk” to each other to realize the ultra-precise measurements that harness the laws of quantum mechanics—quantum metrology.
Last year, O’Brien and his collaborator Professor Takeuchi and co-workers at Hokkaido Univ. reported such a quantum metrology measurement with four photons.
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 meter of optical table. This has made them hard to build and difficult to scale up,” says 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,” adds O’Brien.
The team’s chips, fabricated at CIP Technologies, have dimensions measured in millimeters.
This impressive miniaturization 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 fibers.
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 fibers. By measuring the output of the device they confirmed high-fidelity operation.
In the experimental characterization 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.
The team reported its results in the March 27 Science Express. In addition to O’Brien and Alberto Politi co-authors of the Science paper are Martin Cryan, Professor John Rarity, and Siyuan Yu.
The work was funded by the U.S. government Intelligence Advanced Research Projects Activity (IARPA), the Quantum Information Processing Interdisciplinary Research Collaboration (QIP IRC), the Engineering and Physical Sciences Research Council (EPSRC), and the Leverhulme Trust.
SOURCE: Univ. of Bristol, UK
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