J O'Brien Presentation - Think Small Event
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J O'Brien Presentation - Think Small Event

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BEN Event - 20/04/10 - Think Small, NSQI Building, University of Bristol.

BEN Event - 20/04/10 - Think Small, NSQI Building, University of Bristol.

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  • Moore’s Law PHOTONS
  • Each particle not in a well defined state, but the 2 are perfectly correlated Correlations Unfortunately I can’t show you any pretty pictures
  • Each particle not in a well defined state, but the 2 are perfectly correlated Correlations Unfortunately I can’t show you any pretty pictures
  • The low noise, high speed transmission properties of photons have made them the only sensible approach to quantum communication, and people are now envisaging quantum networks… In 2002 KLM solved the problem of how to get photons to interact without the need for optical non-linearities and thereby proposed a route to all-optical QC These schemes were also of importance to Q Metrology. People have been thinking about Q Metrology for a long time - classically light is a great tool f or precision measurement due to the ease with which sub-wavelength displacements can be measured Geoff Related to lithography
  • We remind ourselves that quantum information can be encoded in the form of a qubit on photons. The Qubit: Two level quantum system. The basic element of quantum information, analagous to the classical bit. This is achieved, for example, in path or in polarization, amongst other methods. The bulk-freespace optical components used for manipulating QI include Waveplate: a birefringent material that alters polarization in a unitary operation by changing relative phase between two orthogonal polarization states. Beam splitter
  • Of the anticipated quantum technologies, photons are essential for communication, an obvious choice for metrology, and a leading approach to information processing. They also have a long history of addressing fundamental scientific questions. Here are some examples of experiments that I have been involved in recently: This 3-photon Toffoli gate builds on my original demonstration of a CNOT gate Beating the standard quantum limit with 4 entangled photons And a quantum filter that operates on entanglement – which is the most sophisticated multi-photon circuit yet built. As with all other work in the field, these experiments use bulk optics bolted to a lab table; inefficient single photon sources based on non-linear crystals; and modest efficiency detectors This approach is of course not ultimately miniaturizable or scalable and is limited in performance. Even in the near term we have reached technical limits: we cannot imagine building things even 2-5 times more complicated than this circuit - never mind 10 or 10,000 times as complicated. Recently in collaboration with John Rarity and others at Bristol I have made some progress in replacing these circuits with optical fibres which I believe has great promise for quantum communication… _____________________________ Anticipated quantum technologies include enhanced communication security, exponential increase in computational power and improved measurement precision. QIS is already answering fundamental questions about entanglement and quantum measurement. these systems have also reached the technical limits of what can be aligned on an optical table – we cannot imagine building things twice as complicated as this,
  • Now we leave the world of bulky optics and move to integrated structures. Grow a layer of silica doped with phosphorous on a pure silica cladding layer. Then use lithography to etch out the waveguide. Then grow more pure silica on top Core 3.5 micron wide. Leaves tracks of a different refractive index in a material of another. Just as with the case of an optical fibre, this guides the field light along the paths in the structure. Square to preserve polarization. Why? The work horse of encoding photons in path in free-space is the beam splitter. This is equivalent to a directional coupler.
  • Politi et al demonstrated that the CNOT can indeed be implemented on an integrated waveguide chip.
  • Politi et al demonstrated that the CNOT can indeed be implemented on an integrated waveguide chip.
  • Politi et al demonstrated that the CNOT can indeed be implemented on an integrated waveguide chip.
  • For experimental quantum applications, this technique is extremely useful and relatively quick method for drawing out waveguide structures. The well established technique of lithographically etching and growing silica on silicon waveguides is an involved process requiring masks to be drawn up and several devices to be made at once to reduce over-all cost. The first step, therefore, is to ensure these glass waveguides behave well in the non-classical regime. We therefore tested several directional coupler devices in a HOM experiment and these are the results.

J O'Brien Presentation - Think Small Event J O'Brien Presentation - Think Small Event Presentation Transcript

    • Integrated quantum photonics
    Jeremy O’Brien NEDQIT € : £: $: ¥:
    • Quantum technologies
    • Photonic approach
    • Quantum circuits on silicon chips
  • Physical is quantum  Quantum information No physical representation  No information No physical process  No processing  Revolution in information and communication technologies “ Information is physical” - Rolf Landauer
  • Quantum mechanics
    • A description of the world at small scales
    • Quantized
    • Inherently uncertain
      • eg . position-momentum ‘uncertainty principle’
    • Very counter intuitive
    • … and very useful
    • Normal bit  quantum bit or ‘ qubit ’:
    • a two-level quantum mechanical system
    • eg. the polarisation of a single photon:
    • Quantum information
    ‘ Superposition’ + JL O’Brien Science , 318 , 5856 (2007) 0 1
    • Entanglement
    • Entanglement
    Entanglement is “ the characteristic trait of quantum mechanics, the one that enforces its entire departure from classical lines of thought.” - Schrödinger, 1935 …
  • Franson Phys. Rev. Lett . 62, 2205–2208 (1989) Communication JL O’Brien, A Furusawa, J Vuckovic Nature Photonics , 3 , 687 (2009) Security based on Physics Lithography Ladd, et al Nature 464, 45 (2010) Computation Tremendous power Metrology Precision measurement
    • Encoding Quantum Information in Photons
    JL O’Brien Science , 318 , 5856 (2007)
  • 2-photon interactions?
  •  
    • Photonic Controlled-NOT gate
    Milburn, PRL 62 , 2124 (1989) Control Target IN OUT 00 00 01 01 10 11 11 10 0 1 Control Target 0 1 Non-linear phase shift
  •  
    • Quantum information with photons
    Knill, Laflamme and Milburn Nature 409 , 46 (2001)
    • Non-classical interference
    x 50% BS P = P( ) + P( )
    • Non-classical interference
    P = | + | 2 50% BS
  • Information processing Lanyon et al. Nature Physics 5 134 (2009) O’Brien , et al. , Nature 426 264 (2003) O’Brien, Science , 318 5856 (2007) Communication Clark, Fulconis, Rarity, Wadsworth, O’Brien Phys. Rev. A 79 030303 (2009) Nagata, Okamoto, O’Brien, Sasaki, Takeuchi Science , 316 726 (2007); NJP 10 073033 (2008) Metrology Entanglement Okamoto, O’Brien, Hofmann, Nagata, Sasaki, Takeuchi Science , 323 483 (2009)
  •  
    • Integrated quantum photonics
    ~25 mm Politi, Cryan, Rarity, Yu, and O’Brien Science, 320 , 5876 (2008)
    • CNOT gate on a chip
    Laing, Peruzzo, Politi, Rodas Verde, Halder, Ralph, Thompson, O’Brien arXiv:1004.0326 Ideal: Expected: Measured: F = 0.969 ± 0.002 S = 0.993 ± 0.002
    • Manipulation of Entanglement on a chip
    Matthews, Politi, Stefanov, and O’Brien Nature Photonics 3 , 346 (2009)
    • Quantum factoring algorithm on a chip
    Politi, Matthews, O’Brien Science 325 1221 (2009)
    • Quantum factoring algorithm on a chip
    Politi, Matthews, O’Brien Science 325 1221 (2009)
    • Quantum walks in SiO x N y
    Peruzzo, Matsuda, Matthews , Politi, Poulios, Lobino, Zhou, Wórhoff, Bromberg, Lahini, Silberberg, Thompson, O’Brien
    • Two- particle quantum walks
    Peruzzo, Matsuda, Matthews , Politi, Poulios, Lobino, Zhou, Wórhoff, Bromberg, Lahini, Silberberg, Thompson, O’Brien
    • Conclusions
    Quantum Communication & Computing Reconfigurable circuits & Precision measurement Quantum simulations +Sources & Detectors