Download Quantum information science with photons on a chip

Quantum information science with photons on a chip
Jeremy L. O’Brien
Centre for Quantum Photonics,
H. H. Wills Physics Laboratory & Department of Electrical Engineering, University of Bristol
www.phy.bris.ac.uk/people/jeremy_obrien/cqp.html
Quantum information science has shown that quantum mechanical effects can dramatically
improve performance for certain tasks in communication, computation and measurement. Of the
various physical systems being pursued, single particles of light – photons – have been widely
used in quantum communication, quantum metrology, and quantum lithography settings. Low
noise (or decoherence) also makes photons attractive quantum bits (or qubits), and they have
emerged as a leading approach to quantum information processing [1,2].
In addition to single photon sources and detectors, photonic quantum technologies require
sophisticated optical circuits involving high-visibility classical and quantum interference with
photons. While a number of photonic quantum circuits have been realized for quantum metrology
[3], quantum lithography, and quantum logic gates [4]. These demonstrations have relied on largescale (bulk) optical elements bolted to large optical tables, thereby making them inherently
unscalable.
Quantum technologies based on photons will likely require an integrated optics architecture for
improved performance, miniaturization and scalability. We demonstrate high-fidelity silica-onsilicon integrated optical realizations of key quantum photonic circuits, including two-photon
quantum interference with a visibility of 94.8(5)%; a controlled-NOT gate with an average logical
basis fidelity of 94.3(2)%; and a path entangled state of two photons, relevant to quantum
metrology, with fidelity >92% [5].
The monolithic nature of these devices means that the correct phase can be stably realized in what
would otherwise be an unstable interferometer, greatly simplifying the task of implementing
sophisticated photonic quantum circuits. We fabricated 100's of devices on a single wafer and find
that performance across the devices is robust, repeatable and well understood. We have also
demonstrated an all optical fibre CNOT gate [6]
These results show that it is possible to directly “write” sophisticated photonic quantum circuits
onto a silicon chip, which will be of benefit to future quantum technologies based on photons, as
well as the fundamental science of quantum optics.
[1] E Knill, R Laflamme, G J Milburn, Nature 409, 46 (2001)
[2] J L O’Brien, Science 318 1567 (2007).
[3] T Nagata, R Okamoto, J L O'Brien, K Sasaki, S Takeuchi Science 316, 726 (2007)
[4] J L O'Brien, G J Pryde, A G White, T C Ralph, D Branning, Nature 426, 264 (2003).
[5] A Politi, M J Cryan, J G Rarity, S Yu, J L O’Brien Science to appear (2008) / arXiv:0802.0136
[6] A S Clark, J Fulconis, J G Rarity, W J Wadsworth, J L O’Brien Nature Physics under review /
arxiv/0802.1676