Quantum metamaterials, quantum imaging, quantum engineering and quantumness Alexandre Zagoskin Department of Physics Loughborough University June 1, 2015 • The fabrication and control of macroscopic artificial quantum structures, such as qubits, qubit arrays, quantum annealers and, recently, quantum metamaterials, have witnessed significant progress over the last 15 years. This was a surprisingly quick evolution from theoretical musings to what can now be called quantum engineering [the observation of such phenomena even in a single superconducting device was considered a truly challenging task in 1980. Today, we stand at the point where existing theoretical and computational tools become inadequate for predicting, analysing, and simulating the behaviour of such structures, in which quantum superposition and entanglement are essential. Quantum metamaterials can play an important role both as a testing ground for the development of such new tools and as a platform for the realization of quantum technologies 2.0. QMM Events • Quantum metamaterials at: ▫ Metamaterials 2011 (Barcelona) ▫ Metamaterials 2012 (Paris) ▫ Metamaterials 2012 (St. Petersburg) ▫ META2012 (Nanjing) ▫ Metamaterials 2013 (Bordeaux) ▫ PIERS 2013 (Taipei) Philosophy of quantum mechanics • Copenhagen interpretation • Many worlds • Environmental decoherence ▫ Quantum Darwinism • • • • Consistent histories Pilot wave ? “Shut up and calculate!” …and all that Capra • All popularizations of quantum mechanics are wrong • Some are much more wrong than others • “Amount of knowledge the ancients did not possess was obviously very significant” Attributed to Mark Twain Philosophy: baggage train of science • …which is necessary and useful, but should never ever be in the lead Copenhagen vs. Schengen quantum-classical boundary Qubits for quantum computing and much, much more Phase qubit: Allman et al., 2010 Charge qubits: Yamamoto et al., 2003 Flux qubits: Grajcar et al., 2006 Why now? • Fabrication of multiqubit arrays with controlled macroscopic quantum coherence now possible • Current theoretical methods at their limit and new approaches are urgently needed • Applications (part of “quantum technologies 2.0”): ▫ ▫ ▫ ▫ Integrated quantum limited detection and image processing Quantum optimization Quantum simulation Quantum communication D-Wave controversy D-Wave controversy • World’s biggest collection of qubits (current version “Washington” has 1152 qubits, 933 operational) • Quantum operation confirmed for 8-qubit register • Operation consistent with both quantum and classical models • Decoherence time of a qubit much shorter than the adiabatic evolution time • How to tell whether it is quantum, and if so, is it quantum enough? • 3000× SNAFU • Recent data (C. Williams at Oxford): N-qubit system with E couplers stays within 𝑁 + 𝐸 from the ground state – consistent with the LZ diffusion picture How far do we get from the initial state? • “LZ diffusion” N – number of anticrossings per energy level Wang L, Roennow T, Boixo S, Isakov S, Wang Z, Wecker D, et al. Comment on: “Classical signature of quantum annealing.” arXiv:1305.5837 (2013). Shin S, Smith G, Smolin J, Vazirani U. How “Quantum” is the D-Wave machine? arXiv:1401.7087 (2014). Grand Challenge Quantum engineering for QT2.0 • Accommodating incompatible requirements • Using “rule-of-thumb” estimates for characterizing and predicting the system’s performance and reliability • Heuristics • Scaling • “Engineering is about building reliable structures using non-reliable components” So, what can we do with many good enough qubits? Metamaterials: artificial optical media • Left-handed MMs ▫ Negative refractive index Superlenses Cloaking • Photonic bandgap MMs ▫ Photonic crystals • Tunable MMs • MM antennas N.I. Zheludev. The Road Ahead for Metamaterials. Science 328, 582 (2010) Quantum metamaterials: • Artificial optical media that have the following properties: ▫ They are composed of quantum coherent unit elements with engineered parameters ▫ Quantum states of these elements can be controlled ▫ The whole structure can maintain global quantum coherence for longer than the traversal time of a relevant electromagnetic signal Rakhmanov, Zagoskin, Saveliev & Nori, Phys. Rev. B 77, 144507 (2008) Quantum metamaterials: a brave new world • Introducing quantum degrees of freedom opens new ways to control light-matter interaction in artificial structures. ▫ D. Felbacq and M. Antezza SPIE Newsroom, 19 June 2012 View from… META’12: Metamaterials mature • Researchers in the field of metamaterials are … tackling new topics such as quantum metamaterials. ▫ David Pile Nature Photonics 6, 419 (2012) • A quantum computer can be considered a special case of a quantum metamaterial QMMs from 2008 to 2014 •Theoretical proposal: •Rakhmanov, Zagoskin, Saveliev & Nori, Phys. Rev. B 77, 144507 (2008) •Zagoskin, Rakhmanov, Saveliev & Nori, Phys. Stat. Solidi B 246, 955 (2009) • (a) (b) Proof of principle: Astafiev, Zagoskin et al., • Science (2010) Experimental prototype: Macha et al. (2013) (d) (c) a 1 m I tI 0 Is Is 0 Non-superconducting platforms: Atom-cavity arrays: Quach et al., 6 June 2011 / Vol. 19, No. 12 / OPTICS EXPRESS 11018 Optical lattices (Miranowicz et al., in progress) NV-centres (Zagoskin et al., in progress) Why are quantum metamaterials interesting? • Macroscopic quantum effects • Testing limits of quantum mechanics • Testing new theoretical methods • Applications Watching a Schrödinger’s cat jump What if instead of scattering a What if instead of scattering a quantum wave off a classical grating quantum wave off a we scatter a classical wave off a quantum grating? classical grating we scatter a wavecase: offthean In this work weclassical considered the simplest propagation of a classical electromagnetic through a 1D object? array of charge qubits. extendedwave quantum ? The simplest case: 1D quantum metamaterial Simplest case: Charge qubit line • Rakhmanov, Zagoskin, Saveliev and Nori, Phys. Rev. B 77, 144507 (2008) Flux qubit line Zagoskin, Rakhmanov, Saveliev and Nori, Phys. Status Solidi B 246, No. 5 (2009) 955 Proof-of-principle test a f0 = 10.204 GHz Ip = 195 nA 1 m (GHz) b 13 1.0 0.8 0.6 0.4 0.2 0 12 I tI 0 Is c Is 0 c 60 -80 t -40 1.200 1.144 30 1.088 1.031 0 1 0.9750 arg(t) -30 0.9188 0.8625 -60 0 40 0.8063 0.8 80 0.7500 (MHz) 0.6938 0.6375 11 t 0.6 0.5813 0.5250 0.4688 0.4125 0.4 0.3563 0.3000 10 -8 -6 -4 -2 0 2 -3 10 4 6 8 Astafiev, Zagoskin et al., Science (2010) Elastic scattering a 0.4 -112 dBm -132 dBm Im (r) 0.2 0.0 -0.2 -122 dBm -0.4 0.0 0.2 0.4 0.6 Re (r) 0.8 0.0 0.2 0.4 0.6 Re (r) 0.8 “Ambidextrous quantum metamaterial” The system can be in a superposition of left- and right-handed states Initialization of a1D quantum metamaterial Shvetsov, Satanin, Nori, Saveliev and Zagoskin (2013) Initialization of a1D quantum metamaterial Shvetsov, Satanin, Nori, Saveliev and Zagoskin (2013) Pulse propagation through the 1D metamaterial 2D and 3D phase-qubit quantum metamaterials Zagoskin, J. Opt. 14 (2012) 114011 Lasing in a 1D quantum metamaterial Asai et al. (2014) Asai et al. (2014) Asai et al. (2014) Josephson-like vortices in a 1D quantum metamaterial Asai et al. (2013) Asai et al. (2014) Asai et al. (2013) Asai et al. (2014) A model system: Cayley tree (aka Bethe lattice) Detecting a single photon’s wavefront Zagoskin, Wilson, Everitt, Saveliev, Gulevich, Allen, Dubrovich and Il’ichev (Scientific Reports, 2013) Model Hamiltonian Signal spectra for coherent (left) and Fock (right) input states “Quantum imaging algorithms” A. Sowa (2014) Hardware implementation: “Quantum perceptron” Rigid quantum metamaterials • (Saveliev and Zagoskin) Rigid quantum metamaterials • (Saveliev and Zagoskin) Unusual unit elements: anapole QMM • (Zagoskin, Shipulin, Il’ichev, Johansson and Nori) Next steps: • A quantitative theory, which will direct experimental effort in QMM and quantum engineering and can only be developed in a close collaboration between theory and experiment Further perspectives • Using quantum engineering to test the limits of quantum mechanics • Realization of quantum metamaterial-based systems for imaging, detection, quantum communications and information processing (in particular, for biomedical applications) ▫ Hypersensitive detectors ▫ Early stage diagnostics • Developing quantum simulators of quantum systems • Developing and protecting intellectual property • Developing spin-offs Conclusions • Research in quantum metamaterials has the potential for both fundamental breakthroughs and developing disruptive new technologies, new IP and business opportunities • The research bridges quantum information science, condensed matter physics, physics of metamaterials, quantum optics, and quantum physics, and is expected to have significant impact on chemical, biological and medical research and technologies • Quantum metamaterials – a natural and most feasible testing ground for the development of quantum engineering