LPHYS'22.    Plenary Speakers:

  1. Quantifying Quantum Metrology: Noiseless Amplification, Precision Bounds For Open Systems, and Ghost Quantum Sensing

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      Luis Davidovich

      Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
      Institute for Quantum Science and Engineering, Texas A&M University, College Station, TX, USA

    Quantum metrology is one of the basic pillars of quantum information, together with quantum computation, quantum simulation, and quantum communication. It concerns the estimation of parameters, for which lower bounds to the precision of estimation are derived through a rigorous theoretical framework, established by Cramér, Rao, and Fisher for classical systems and generalized to quantum physics by Helstrom and Holevo. This framework yields simple expressions for the precision when dealing with parameter-dependent unitary evolutions in closed systems. Open systems, on the other hand, require more sophisticated techniques [1-4]. This talk reviews recent results on closed and open systems: the analysis of an experiment on noiseless quantum amplification of mechanical oscillator motion [5,6], and the demonstration that, for open systems, a procedure analogous to quantum ghost imaging may increase the precision of estimation.

    [1] B. M. Escher, R. L. de Matos Filho, and L. Davidovic, Nature Physics 7, 406 (2011).
    [2] B. M. Escher, L. Davidovich, N. Zagury, and R. L. de Matos Filho, Phys. Rev. Lett. 109, 190404 (2012).
    [3] C. L. Latune, B. M. Escher, R. L. de Matos Filho, and L. Davidovich, Phys. Rev. A 88, 042112 (2013).
    [4] J. Wang, L. Davidovich, and G. S. Agarwal, Phys. Rev. Research 2, 033389 (2020).
    [5] S. C. Burd, R. Srinivas, J. J. Bollinger, A. C. Wilson, D. J. Wineland, D. Leibfried, D. H. Slichter, and D. T. C. Allcock, Science 364, 1163 (2019).
    [6] G. S. Agarwal and L. Davidovich, Phys. Rev. Research 4, L012014 (2022).

  2. From Multi-Photon Entanglement to Quantum Computational Advantage

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      Jian-Wei Pan

      University of Science and Technology of China, Hefei, Anhui, China

    Photons, the fast flying qubits which can be controlled with high precision using linear optics and have weak interaction with environment, are the natural candidate for quantum communications. By developing a quantum science satellite Micius and exploiting the negligible decoherence and photon loss in the out space, practically secure quantum cryptography, entanglement distribution, and quantum teleportation have been achieved over thousand kilometer scale, laying the foundation for future global quantum internet. Surprisingly, despite the extremely weak optical nonlinearity at single-photon level, an effective interaction between independent indistinguishable photons can be effectively induced by a multi-photon interferometry, which allowed the first creation of multi-particle entanglement and test of Einstein’s local realism in the most extreme way. By developing high-performance quantum light sources, the multi-photon interference has been scaled up to implement boson sampling with up to 76 photons out of a 100-mode interferometer, which yields a Hilbert state space dimension of 1030 and a rate that is 1014 faster than using the state-of-the-art simulation strategy on supercomputers. Such a demonstration of quantum computational advantage is a much-anticipated milestone for quantum computing. The special-purpose photonic platform will be further used to investigate practical applications linked to the Gaussian boson sampling, such as graph optimization and quantum machine learning.

  3. Quantum Optics with Giant Atoms: Decoherence-Free Interaction between Giant Atoms in Waveguide Quantum Electrodynamics

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      Franco Nori

      Theoretical Quantum Physics Laboratory, Center for Quantum Computing, RIKEN, Japan
      University of Michigan, Ann Arbor, MI, USA

    In quantum optics, atoms are usually approximated as point-like compared to the wavelength of the light they interact with. However, recent advances in experiments with artificial atoms built from superconducting circuits have shown that this assumption can be violated. Instead, these artificial atoms can couple to an electromagnetic field in a waveguide at multiple points, which are spaced wavelength distances apart. Such systems are called giant atoms. They have attracted increasing interest in the past few years (e.g., see the review in [1]), in particular because it turns out that the interference effects due to the multiple coupling points allow giant atoms to interact with each other through the waveguide without losing energy into the waveguide (theory in [2] and experiments in [3]). This talk will review some of these developments. Finally, we will also show how a giant atom coupled to a waveguide with varying impedance can give rise to chiral bound states [4].

    [1] A.F. Kockum, Quantum optics with giant atoms -- the first five years, https://arxiv.org/abs/1912.13012
    [2] A.F. Kockum, G. Johansson, F. Nori, Phys. Rev. Lett. 120, 140404 (2018)
    [3] B. Kannan, M. J. Ruckriegel, D. L. Campbell, A. F. Kockum, J. Braumüller, D. K. Kim, M. Kjaergaard, P. Krantz, A. Melville, B. M. Niedzielski, A. Vepsäläinen, R. Winik, J. L. Yoder, F. Nori, T. P. Orlando, S. Gustavsson, and W. D. Oliver, Nature 583, pp. 775 (2020)
    [4] X. Wang, T. Liu, A.F. Kockum, H.R. Li, F. Nori, Phys. Rev. Lett. 126, 043602 (2021). [PDF]