Kavli Nanoscience Seminar

Time: 16:00 hrs

location: Zaal E, Delft

**abstract**

Of the leading approaches to quantum computing [1], photons are particularly attractive for their low-noise properties and ease of manipulation at the single qubit level [2]. Encoding quantum information in photons is also an appealing approach to quantum communication, metrology (eg. [3]), measurement (eg. [4]) and other quantum technologies [5]. However, the implementation of optical quantum circuits with bulk optics has reached practical limits. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturisation and scalability [6]. This approach has led to high-fidelity silica-on-silicon integrated optical realisations of key quantum photonic circuits, including two-photon quantum interference and a controlled-NOT logic gate [7]. We have demonstrated controlled manipulation of up to four photons on-chip, including high-fidelity single qubit operations, using a lithographically patterned resistive phase shifter [8]. We have used this architecture to implement a small-scale compiled version of Shor’s quantum factoring algorithm [9] and demonstrated heralded generation of tuneable four photon entangled states from a six photon input [10]. We have combined waveguide photonic circuits with superconducting single photon detectors [11] and have demonstrated how quantum process discrimination can be implemented with photonic circuits [12]. Here we will focus on our most recent results on complex quantum interference in multi-mode interference devices with up to eight inputs and outputs [13], quantum walks of correlated particles in arrays of coupled waveguides [14], the development and implementation of a scheme that dramatically improves implementation of quantum logic circuits by harnessing entanglement on non-computational degrees of freedom [15], and strongly enhanced photon collection from diamond colour centres under micro-fabricated integrated solid immersion lenses [16].

[1] T. D. Ladd, F. Jelezko, R. Laflamme, Y. Nakamura, C. Monroe, and J. L. OBrien, Nature 464, 45 (2010).

[2] J. L. O’Brien, Science 318, 1567 (2007). [3] T. Nagata, R. Okamoto, J. L. O’Brien, K. Sasaki, and S. Takeuchi, Science 316, 726 (2007).

[4] R. Okamoto, J. L. O’Brien, H. F. Hofmann, T. Nagata, K. Sasaki, and S. Takeuchi, Science 323, 483 (2009).

[5] J. L. O’Brien, A. Furusawa, and J. Vuc?kovic ?, Nature Photon. 3, 687 (2009).

[6] A. Politi, M. J. Cryan, J. G. Rarity, S. Yu, and J. L. O’Brien, Science 320, 646 (2008).

[7] A. Laing, A. Peruzzo, A. Politi, M. R. Verde, M. Halder, T. C. Ralph, M. G. Thompson, and J. L. O’Brien, Appl. Phys. Lett., in press; arXiv:1004.0326 .

[8] J. C. F. Matthews, A. Politi, A. Stefanov, and J. L. O’Brien, Nature Photon. 3, 346 (2009).

[9] A. Politi, J. C. F. Matthews, and J. L. O’Brien, Science 325, 1221 (2009).

[10] J. C. F. Matthews, A. Peruzzo, D. Bonneau, and J. L. O’Brien, arXiv:1005.5119.

[11] C. M. Natarajan, A. Peruzzo, S. Miki, M. Sasaki, Z. Wang, B. Baek, S. Nam, R. H. Hadfield, and J. L. O’Brien, Appl. Phys. Lett. 96, 211101 (2010).

[12] A. Laing, T. Rudolph, and J. L. O’Brien, Phys. Rev. Lett. 102, 160502 (2009).

[13] A. Laing, A. Peruzzo, A. Politi, M. Rodas Verde, M. Halder, T. C. Ralph, M. G. Thompson, and J. L. O'Brien, arXiv:1006.2093.

[14] A. Peruzzo, M. Lobino, J. C. F. Matthews, N. Matsuda, A. Politi, K. Poulios, X.-Q. Zhou, Y. Lahini, N. Ismail, K. Wörhoff, Y. Bromberg, Y. Silberberg, M. G. Thompson, and J. L. O'Brien,Science 329, 1500 (2010) [15] X.-Q.Zhou, T. C. Ralph, P. Kalasuwan, M. Zhang, A. Peruzzo, B. P. Lanyon, and J. L. O'Brien, arXiv:1006.2670 [16] J. P. Hadden, J. P. Harrison, A. C. Stanley-Clarke, L. Marseglia, Y.-L. D. Ho, B. R. Patton, J. L. OBrien, and J. G. Rarity, Appl. Phys. Lett., in press; arXiv:1006.2093.