2020:

    • Name: Dr. Zhaohui Wei
    • Dates for visit(online): 2pm, 22nd October 2020 (UTC+8) Zoom link
    • Unit: Tsinghua University
    • Talks in IFFS:
      • Quantifying unknown entanglement in a device-independent manner
        • Abstract:

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          Certifying unknown quantum entanglement experimentally is a fundamental problem in quantum information. However, due to the imperfection of quantum operations, this is a very challenging task, not to mention quantifying unknown (multipartite) entanglement experimentally. Fortunately, it turns out these two tasks can be fulfilled reliably and efficiently using device-independent approaches, where the certification and quantification are achieved based on the observed nonlocality only and one does not have to care about the precision and internal workings of involved quantum devices. In this talk, we will introduce several recent progresses on this problem.

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    • Name: Dr. Lorenzo Maccone
    • Dates for visit(online): 3pm, 15th October 2020 (UTC+8) Zoom link
    • Unit: University of Pavia, Italy
    • Talks in IFFS:
      • Squeezing Metrology: a unified framework
        • Abstract:

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          I will briefly introduce quantum metrology and then focus on quantum metrology for squeezing. Usually the theory uses the resolution gains obtainable thanks to the entanglement among N probes. Typically, a quadratic gain in resolution is achievable, going from the 1/\sqrt(N) of the central limit theorem to the 1/N of the Heisenberg bound. We focus on quantum squeezing and provide a unified framework for metrology with squeezing, showing that, similarly, one can generally attain a quadratic gain when comparing the resolution achievable by a squeezed probe to the best N-probe classical strategy achievable with the same energy. Namely, here we give a quantification of the Heisenberg squeezing bound for arbitrary estimation strategies that employ squeezing. Our theory recovers known results (e.g. in quantum optics and spin squeezing), but it uses the general theory of squeezing and holds for arbitrary quantum systems. The talk is based on the paper:
          L. Maccone, A. Riccardi, Squeezing Metrology: a unified framework, Quantum 4, 292 (2020).

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    • Name: Dr. Tony J. G. Apollaro
    • Dates for visit(online): 3pm, 9th October 2020 (UTC+8) Zoom link
    • Unit: Department of Physics, University of Malta
    • Talks in IFFS:
      • Many qubit quantum state transfer and routing via resonant tunnelling in spin chains
        • Abstract:

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          Quantum-State Transfer (QST) is an important requisite in many Quantum Information Processing (QIP) protocols [1]. For short-distance communication, interacting spin-1/2 chains as a data bus fulfilling faithful QST between a sender and a receiver qubit have been widely investigated and different protocols have been proposed. A step forward would be to allow for the use of a single data bus by many senders and receivers for QIP protocols. In this talk a protocol for high-fidelity QST from one sender to a selected receiver out of many possible ones is proposed by exploiting a weak-coupling mechanics inducing resonant tunnelling of the excitation between the sender and the selected receiver location. The same protocol is also explored in order to achieve QST of more than a single qubit [2], generation of multiple pairs of Bell states [3], and transfer of multipartite entanglement [4].
          Reference:
          [1] S. Bose (2007) Quantum communication through spin chain dynamics: an introductory overview, Contemporary Physics, 48:1, 13-30, http://dx.doi.org/10.1080/00107510701342313
          [2] W.J. Chetcuti, C. Sanavio, S. Lorenzo and T.J.G. Apollaro, Perturbative many-body transfer, 2020 New J. Phys. 22 033030 https://doi.org/10.1088/1367-2630/ab7a33
          [3] T.J.G. Apollaro, G.M.A. Almeida, S. Lorenzo, A. Ferraro, and S. Paganelli, Spin chains for two-qubit teleportation, Phys. Rev. A 100, 052308 (2019) https://doi.org/10.1103/PhysRevA.100.052308
          [4] T.J.G. Apollaro, C. Sanavio, W.J. Chetcuti, S. Lorenzo, Multipartite entanglement transfer in spin chains, Physics Letters A 384, 126306 2020 https://doi.org/10.1016/j.physleta.2020.126306ony

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    • Name: Dr. Ali Rezakhani
    • Dates for visit(online): 2pm, 24th September 2020 (UTC+8) Zoom link
    • Unit: Sharif University of Technology, Iran
    • Talks in IFFS:
      • Dynamics of Open Quantum Systems from a Correlation Perspective
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          Isolating a quantum system from ambient environment is practically impossible. Interaction with the environment makes obtaining an exact master equation for the dynamics of an open system hard. Most of the existing techniques for deriving a dynamical master equation for an open system are approximative and based on weak-coupling expansions. I give a brief review of such techniques and in particular how the celebrated Lindblad equation is obtained under the weak-coupling, Markovian assumption. I then introduce a novel correlation picture which enables us to derive an exact Lindblad-like master equation, with system-environment correlations included. I also introduce a weak-correlation expansion that allows to perform systematic perturbative approximations. This expansion provides approximate master equations which can feature advantages over existing weak-coupling techniques in the sense that they are more accurate or as accurate as weak-coupling master equations.

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    • Name: Dr. Luis Correa
    • Dates for visit(online): 3pm, 17th September 2020 (UTC+8) Zoom link
    • Unit: University of Exeter, UK
    • Talks in IFFS:
      • Getting “quantum” about thermometry
        • Abstract:

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          Recent experimental advances have made record-breaking cooling possible in ultracold gases. And yet, state-of-the-art thermometric techniques fall short of the challenge of measuring their temperatures with high accuracy in the subnanokelvin range. The limitations are not just technical—there are stringent fundamental bounds on the precision of low-temperature thermometry. To approach them as closely as possible, it becomes necessary to revise every step in the estimation process: from the design of the probe, to the choice of temperature estimator, and the physical modelling of probe and sample, which dictates how the measured data must be processed into a temperature estimate. The emerging field of quantum thermometry aims at answering these questions, by blending quantum parameter estimation with the theory of open quantum systems. In this talk I will give an overview of the field and focus on applications to impurity thermometry in ultracold atomic gases.

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    • Name: Dr. Rubem Mondaini
    • Dates for visit(online): 2pm, 10th September 2020 (UTC+8) Zoom link
    • Unit: Beijing Computational Science Research Center, China
    • Talks in IFFS:
      • Many-body localization: When thermalization fails and how to experimentally observe it
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          The observation of many-body localization is a paradigmatic example of the amount of time an idea takes to get mature enough, and the numerical and experimental methods to sufficiently develop, in order to settle its existence. After the original study of Philip Anderson in 1958, demonstrating localization of non-interacting quantum particles in disordered settings, a natural question is on the resulting effects of the inter-particle interactions on this phenomenon. Only after 50 years, substantial theoretical progress was made in solving this puzzle and, in 2016 the first experimental observation of this phenomenon was realized. The advent of platforms involving ultracold atoms trapped by optical lattices allowed the inspection of an inherently dynamical quantum phase transition, that goes beyond the standard ground-state classification of the quantum matter, and its associated low-lying excitations. Instead, it is described by a high-energy phase transition, inherently manifested via the unitary dynamics of an isolated quantum system, wherein by tuning the strength of disorder, one is able to halt the onset of ergodic behavior and thermalization. In this talk, after introducing the general conditions where it occurs, and review the experiments tackling it so far, I will show numerical and experimental results using quantum circuits of superconducting qubits that shed light on yet another highly debated aspect: the possible existence of many-body mobility edges.
          Reference: arXiv preprint, arXiv:1912.02818, “Observation of energy resolved many-body localization”, Qiujiang Guo, Chen Cheng, Zheng-Hang Sun, Zixuan Song, Hekang Li, Zhen Wang, Wenhui Ren, Hang Dong, Dongning Zheng, Yu-Ran Zhang, Rubem Mondaini, Heng Fan, H. Wang. — Nature Physics (in press)

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    • Name: Dr. Amir Mohammadi
    • Dates for visit(online): 3pm, 3rd September 2020 (UTC+8) Zoom link
    • Unit: Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Germany
    • Talks in IFFS:
      • Towards simulating of chemical reactions at the quantum limits
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          The rates of chemical reactions are predicted to be increased rapidly at very low temperatures where the quantum mechanical treatments start dominating the classical processes. In such an interaction regime, one can get precise control over the chemical processes by finding a full understanding from the dynamics of involved parameters acting on the reactions, including but not limited to initial quantum states of the reactants and applied external fields. The system under investigation can be even more complicated if reactants are molecules with microscopic degrees of freedom. In this work, we show how such a system can be simulated via a hybrid atom-ion system in which the dynamics and evolution of a single molecular ion inside a bath of ultracold neutral Rb atoms are investigated at very low collision energies of a few mK.

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    • Name: Dr. Kishor Bharti
    • Dates for visit(online): 2pm, 27th August 2020 (UTC+8) Zoom link
    • Unit: Center for Quantum Technologies, Singapore
    • Talks in IFFS:
      • Near-term quantum algorithms for linear systems of equations
        • Abstract:

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          Solving linear systems of equations is essential for many problems in science and technology, including problems in machine learning. Existing quantum algorithms have demonstrated the potential for large speedups, but the required quantum resources are not immediately available on near-term quantum devices. In this work, we study near-term quantum algorithms for linear systems of equations of the form Ax = b. We investigate the use of variational algorithms and analyze their optimization landscapes. There exist types of linear systems for which variational algorithms designed to avoid barren plateaus, such as properly initialized imaginary time evolution and adiabatic-inspired optimization, suffer from a different plateau problem. To circumvent this issue, we design near-term algorithms based on a core idea: the classical combination of variational quantum states (CQS). We exhibit several provable guarantees for these algorithms, supported by the representation of the linear system on a so-called Ansatz tree. The CQS approach and the Ansatz tree also admit the systematic application of heuristic approaches, including a gradient-based search. We have conducted numerical experiments solving linear systems as large as 2 300 × 2 300 by considering cases where we can simulate the quantum algorithm efficiently on a classical computer. These experiments demonstrate the algorithms’ ability to scale to system sizes within reach in near-term quantum devices of about 100-300 qubits.

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    • Name: Dr. Tommaso Macrì
    • Dates for visit(online): 5pm, 20th August 2020 (UTC+8) Zoom link
    • Unit: Universidade Federal do Rio Grande do Norte, Natal, Brazil
    • Talks in IFFS:
      • Superfluidity and quasicrystals with nonlocal interactions
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          In recent years, propelled by the progress in the field of quantum simulations with ultracold atoms, there has been an increasing interest of the condensed matter community in what is generally called quasicrystal lattices, long-range ordered but non-periodic structures. Besides retaining intrinsic relevant questions that range from the stability of tiled structures at zero temperature to their relation to fractal lattices, quasicrystals have also shown to support quantum phases of matter such as superconductors and Bose-Einstein condensates. Nonetheless, in spite of important works that address the emergence of quasicrystalline order in classical systems, a deeper understanding of the role of quantum fluctuations in these structures still lacks. Here we present our proposal to realize quasi-crystalline states in ultra cold setups with non-local interactions.

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    • Name: Dr. Nana Liu
    • Dates for visit(online): 13th August 2020
    • Unit: Shanghai Jiao Tong University
    • Talks in IFFS:
      • Adversarial quantum learning
        • Abstract:

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          In the classical world, there is a powerful interplay between security and machine learning deployed in a network, like on the modern internet. What happens when the learning algorithms and the network itself can be quantum? What are the new problems that can arise and can quantum resources offer advantages to their classical counterparts?
          We explore these questions in a new area called adversarial quantum learning, that combines the area of adversarial machine learning, which investigates security questions in machine learning, and quantum information.
          For the first part of the talk, I’ll introduce adversarial machine learning and some exciting potential prospects for contributions from quantum information and computation. For the second part of the talk, I’ll present two recent works on adversarial quantum learning. Here we are able to quantify the vulnerability of quantum algorithms for classification against adversaries and learn how to leverage quantum noise to improve its robustness against attacks.

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    • Name: Dr. Xingyao Wu
    • Dates for visit(online): 10th August 2020
    • Unit: HiQ team in Huawei
    • Talks in IFFS:
      • An introduction to Huawei’s HiQ simulator and quantum research
        • Abstract:

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          HiQ is Huawei’s high-performance cloud platform for large-scale quantum circuit simulations based on HUAWEI CLOUD’s powerful computing and storage infrastructure. It plays an important role in quantum hardware design and verification, quantum algorithm research and quantum software design. The world largest VQE simulation has been carried out on HiQ (in terms of number of orbitals). In this talk, I’ll introduce the basic functionalities of HiQ and its application scenarios. I’ll also briefly introduce our recent research on quantum chemistry VQE and quantum optimization.

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    • Name: Dr. Tao Wang
    • Dates for visit(online): 30th July 2020
    • Unit: Department of Physics, and Center of Quantum Materials and Devices, Chongqing University (重庆大学)
    • Talks in IFFS:
      • Floquet engineering on Sr-87 optical lattice clock platform
        • Abstract:

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          Floquet engineering is a powerful tool to customize quantum states and Hamiltonians via time-periodic fields. On the other hand, the optical lattice clock (OLC) is among the most accurate precision measurement devices. Considering the long life time of the clock state, the OLC becomes an ideal candidate for Floquet engineering the internal (atomic) energy distribution. In this talk, I will introduce the theoretical and experimental research on this project. Our work aims to design of a new generation of devices for sensing, metrology and simulating exotic spin-orbit Hamiltonian.

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2019:

    • Name: Xuefeng Zhang (张学锋)
    • Dates for visit: 27th June 2019 – 28th June 2019
    • Unit: Chongqing University (重庆大学)
    • Talks in IFFS:
      • Frustrated optical lattice: from topological excitations to deconfined phase transition
      • Machine learning of quantum phase transitions

    • Name: Chiranjib Mukhopadhyay
    • Dates for visit: 11st July 2019 – 15th July 2019
    • Unit: Harish-Chandra Research Institute
    • Talks in IFFS:
      • Thermometric schemes using superposition of temporal order and weak measurement

    • Name: Matteo Paris
    • Dates for visit: 13rd July 2019 – 20th July 2019
    • Unit: Harish-Chandra Research Institute
    • Talks in IFFS:
      • Universal Quantum Magnetometry with Spin States at Equilibrium
      • Quantum sensing and metrology: the quantum Cramer-Rao bound and beyond

    • Name: Haidong Yuan (袁海东)
    • Dates for visit: 22nd July 2019 – 25th July 2019
    • Unit: The Chinese University of Hong Kong (香港中文大学)
    • Talks in IFFS:
      • Ultimate precision limit for quantum parameter estimation

    • Name: John Charles Mcintosh Gray
    • Dates for visit: 22nd Sep 2019 – 29th Sep 2019
    • Unit: Imperial College London
    • Talks in IFFS:
      • Tensor Network Tomography
      • Tensor Network Basics
      • Tensor Network Algorithms

    • Name: Mikio Nakahara + Shingo Kukita
    • Dates for visit: 24th Nov 2019 – 27th Nov 2019
    • Unit: Shanghai University (上海大学)
    • Talks in IFFS:
      • Spin-selective electron transfer in a quantum dot array
      • An upper bound on the number of compatible parameters in simultaneous quantum estimation

    • Name: Marc-Antoine Lemonde
    • Dates for visit: 26th Nov 2019 – 1st Dec 2019
    • Unit: National University of Singapore
    • Talks in IFFS:
      • Phonon Networks with Silicon-Vacancy Centers in Diamond Waveguides

    • Name: Yuji Hirono
    • Dates for visit: 16th Dec 2019 – 21st Dec 2019
    • Unit: Asia Pacific Center for Theoretical Physics (South Korea)
    • Talks in IFFS:
      • Topological order, higher-form symmetry, and dense quark matter
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