Photonic quantum technologies

Of the approaches to quantum computing [1], photons are appealing for their low-noise properties and ease of manipulation [2], and relevance to other quantum technologies [3], including communication, metrology [4] and measurement [5]. We report an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability [6--10]. We address the challenges of scaling up quantum circuits using new insights into how controlled operations can be efficiently realised [11], demonstrating Shor's algorithm with consecutive CNOT gates [12] and the iterative phase estimation algorithm [13]. We have shown how quantum circuits can be reconfigured, using thermo-optic phase shifters to realise a highly reconfigurable quantum circuit [14], and electro-optic phase shifters in lithium niobate to rapidly manipulate the path and polarisation of telecomm wavelength single photons [15]. We have addressed miniaturisation using multimode interference architectures to directly implement NxN Hadamard operations [16], and by using high refractive index contrast materials such as SiO$_{\mathrm{x}}$N$_{\mathrm{y}}$, in which we have implemented quantum walks of correlated photons [17], and Si, in which we have demonstrated generation of orbital angular momentum states of light [18]. We have incorporated microfluidic channels for the delivery of samples to measure the concentration of a blood protein with entangled states of light [19]. We have begun to address the integration of superconducting single photon detectors [20] and diamond [21,22] and non-linear [23,24] single photon sources. Finally, we give an overview of recent work on fundamental aspects of quantum measurement, including a quantum version of Wheeler's delayed choice experiment [25].\\[4pt] [1] TD Ladd, \textit{et al} \textbf{\textit{Nature }}\textbf{464}, 45 (2010) [2] JL O'Brien, \textbf{\textit{Science}}\textbf{ 318}, 1567 (2007) [3] JL O'Brien, A Furusawa, J Vuckovic \textbf{\textit{Nature Photon.}}\textbf{ 3}, 687 (2009 [4] T Nagata, \textit{et al} \textbf{\textit{Science}}\textbf{ 316}, 726 (2007) [5] R Okamoto, \textit{et al} \textbf{\textit{Science}}\textbf{ 323}, 483 (2009) [6] A Politi, \textit{et al} \textbf{\textit{Science }}\textbf{320}, 646 (2008). [7] A Laing, \textit{et al} \textbf{\textit{Appl. Phys. Lett.}}\textbf{ 97}, 211109 (2010) [8] JCF Matthews, \textit{et al} \textbf{\textit{Nature Photon.}}\textbf{ 3}, 346 (2009) [9] A Politi, \textit{et al} \textbf{\textit{Science}}\textbf{ 325}, 1221 (2009) [10] JCF Matthews, \textit{et al} \textbf{\textit{Phys. Rev. Lett.}} \quad \textbf{107}, 163602 (2011) [11] X-Q Zhou, \textit{et al} \textbf{\textit{Nature Comm. }}\textbf{2} 413 2011 [12] E Mart\'{\i}n-L\'{o}pez, \textit{et al} \textbf{\textit{Nature Photon. }}\textbf{6}, 773 (2012) [13] X-Q Zhou, \textit{et al} arXiv:1110.4276 [14] PJ Shadbolt, \textit{et al }\textbf{\textit{Nature Photon.}} \textbf{6}, 45 (2012). [15] D. Bonneau, \textit{et al.} \textbf{\textit{Phys. Rev. Lett.}}, 108, 053601 (2012) [16] A Peruzzo, \textit{et al} \textbf{\textit{Nature Comm.}}\textbf{ 2,} 224 (2011) [17] A Peruzzo, \textit{et al} \textbf{\textit{Science }}\textbf{329}, 1500 (2010) [18] X Cai, \textit{et al }\textbf{\textit{Science}} \quad \textbf{338}, 363 (2012) [19] A Crespi, \textit{et al} \textbf{\textit{Appl. Phys. Lett. }}\textbf{100}, 233704 (2012) [20] CM Natarajan, \textit{et al} \textbf{\textit{Appl. Phys. Lett.}}\textbf{ 96}, 211101 (2010) [21] JP Hadden, \textit{et al }\textbf{\textit{Appl. Phys. Lett.}}\textbf{ 97}, 241901 (2010) [22] L Marseglia, \textit{et al} \textbf{\textit{Appl. Phys. Lett. }}\textbf{98}, 133107 (2011) [23] C. Xiong, \textit{et al.} \textbf{\textit{Appl. Phys. Lett.}}\textbf{ 98}, 051101 (2011) [24] M. Lobino, \textit{et al}, \textbf{\textit{Appl. Phys. Lett. }}\textbf{99}, 081110 (2011) [25] E. Engin, \textit{ et al.} arXiv:1204.4922 [25] A. Peruzzo, \textit{et al} \textbf{\textit{Science}} \textbf{338}, 634 (2012)