An international team of quantum and optical communication scientists involving groups from University of Bristol, Technical University of Denmark, and groups from China, Spain, Germany, and Poland, have realised an advanced large-scale silicon photonic device that allows for processing of quantum information on a hitherto unseen scale. While more common quantum hardware approaches rely on entangling binary (i.e. only 2 states) particles, here the team has found a way to generate and entangle pairs of particles that each have 15 states, promising higher efficiency and noise resilience for quantum applications such as quantum communication and quantum computation.
Technologies relying on quantum mechanics are steadily becoming a bigger and bigger part of our daily lives—this includes lasers, transistors, semiconductor devices, MRI imaging systems and may others, which are often referred to as being part of the first quantum wave (or quantum revolution), ‘quantum1.0’. The next generation of quantum technologies will be embedded even deeper in quantum mechanics, where not merely the devices but the applications will be quantum. Such ‘quantum2.0’ applications include quantum computing, quantum communications and quantum sensing.
Quantum computers are expected to be orders of magnitude faster at solving certain problems than conventional computers. Quantum communications deals with transmitting quantum states (the information) from point A to point B (or from Alice to Bob), and can e.g. in principle ensure unconditionally secure communication links. Quantum information is most often encoded in a binary quantum state (i.e. the particle can be prepared in one of two states corresponding to a 1 and a 0, or indeed in a superposition of these two states, which is unique to quantum systems), referred to as a qubit. Going beyond binary quantum bits (qubits), where the particle may be prepared in several states, one is able to increase the information rate carried by the particle. This is referred to as high-dimensional quantum bits (qudits), and such high-dimensional quantum technology holds the promise for increased quantum information efficiency, noise resilience, communication speed, etc., paving the way for many ground breaking real-life applications.
Manipulation of high-dimensional quantum states is very challenging, though, requiring highly stable and precise control of many components affecting the quantum states. Integrated Quantum Photonics allows for the routing and control of single particles of light with intrinsically high stability and precision. However, to date, this approach has been limited to small-scale demonstrations with only a small number of components integrated on a chip.
Now a group of quantum and optical communications scientists have developed a record-breaking integrated quantum photonic chip counting 550 optical components and enabling 15-dimensional qudits, which will be presented in the journal Science Thursday 8’th March 2018.
The team consists of researchers from Denmark, UK, China, Spain and Poland. The DNRF Centre of Excellence Silicon Photonics for Optical Communications (SPOC) at the Technical University of Denmark fabricated the quantum photonic chip, which is the first ever large-scale integrated quantum photonic circuit. The chip includes 16 identical photon-pair sources, 93 thermo-optical phase-shifters, 122 multimode interferometer (MMI) beamsplitters, 256 waveguide-crossers and 64 optical grating couplers. With this chip, researchers from the Quantum Engineering Technology Labs at the University of Bristol realized the generation, manipulation and analysis of high-dimensional (up to 15-d) entanglement with record-high fidelity and an unprecedented level of precision.
To achieve this, the expertise from several renowned institutions came into play, and the contributors to this work came from the Technical University of Denmark, the University of Bristol, Peking University, Institut de Ciencies Fotoniques (ICFO), the Max Planck Institute (MPI), the Polish Academy of Sciences (PAS) and University of Copenhagen.
Lead author, Dr Jianwei Wang from University of Bristol: “It is the maturity of today’s silicon-photonics that allows us to scale up complexity and reach such a large-scale integration of quantum circuits. This is the most beautiful thing of quantum photonics on silicon. As a result, our quantum chip allows us to, for the first time, reach an unprecedented high precision and universality of controlling multidimensional entanglement, a key factor in many quantum information tasks of computing and communication.”
Corresponding author, senior researcher Dr. Yunhong Ding from SPOC at DTU: “New technologies always enable new applications. The capabilities of our silicon photonics integrated technologies at DTU allow for large scale, highly stable quantum information processing chips, which enable us to observe high-quality multidimensional quantum correlations including generalized Bell and EPR steering violations, and also to implement experimentally unexplored multidimensional quantum protocols: multidimensional randomness expansion and state self-testing.”
Prof. Leif Katsuo Oxenløwe from DTU, Centre leader of SPOC: “The future of silicon photonics is very promising for many both classical and quantum applications. Today we are faced by many urgent challenges including the energy consumption of classical communication networks, and waning security in communication links, and quantum technologies can play a big role in the solutions here. Quantum2.0 has been up and coming for many years now, and with the demonstration of this integrated quantum chip we hope to push the development of scalable quantum information processing units closer to real-life applications. This could have profound impact on e.g. quantum communication links and secure communications.”
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Paper:
‘Multidimensional quantum entanglement with large-scale integrated optics’ by J. Wang, S. Paesani, Y. Ding, R. Santagati, P. Skrzypczyk, A. Salavrakos, J. Tura, R. Augusiak, L. Mancinska, D. Bacco, D. Bonneau, J. W. Silverstone, Q Gong, A. Acin, K. Rottwitt, L. K. Oxenløwe, J. L. O’Brien, A. Laing, and M. G. Thompson in Science.
More information and a copy of the paper, can be found online at the Science press package at http://www.eurekalert.org/jrnls/sci