# Speakers & Participants

#### Serge Haroche *(Collège de France and Ecole Normale Supérieure, Paris)*

**Juggling with photons in cavities**

The founders of quantum theory assumed in thought experiments that they were manipulating isolated quantum systems obeying the counterintuitive laws which they had just discovered. Technological advances have recently turned these virtual experiments into real ones by making possible the actual control of isolated quantum particles. In Paris, we perform such experiments by juggling with photons trapped between superconducting mirrors. We count these photons in a non-destructive way, we observe field quantum jumps and we prepare states of the quantum field reminiscent of the famous cat which Schrödinger imagined to be suspended between life and death. We also learn to use quantum feedback procedures to combat the effects of decoherence phenomena which tend to destroy rapidly the non-classical features of the photonic quantum states. I will give a simple description of these studies, compare them to similar ones performed on other systems and guess about possible applications.

#### Klaus Mølmer *(Aarhus University, Denmark)*

##### Past states of probed quantum systems: “spooky action in the past?” (Slides)

We discuss a new element in the description of open quantum system: the past quantum state [1,2].

This theory extends the stochastic theory of quantum states which evolve subject to measurements in a very special manner: Based on the random outcomes of measurements, we update not only the current state, but we also update what we (now) believe was the state of the quantum system in the past. We derive the central equations of evolution of the past quantum state and we illustrate the application of the theory by analyses of cavity QED experiments performed in Paris [3] and Bonn [4]. Finally, we comment on how the past quantum state may be used to extract information from data with higher precision than conventional analyses.

- S. Gammelmark, B. Julsgaard, and K. Mølmer, Phys. Rev. Lett.
**111**, 160401 (2013). - M. Tsang, Phys. Rev. Lett. 102, 250403 (2009); Phys. Rev. A 80, 033840 (2009); Phys. Rev. A 81, 013824; M. Tsang, H. M. Wiseman, and C. M. Caves, Phys. Rev. Lett. 106, 090401 (2011).
- S. Gleyzes, S. Kuhr, C. Guerlin, J. Bernu, S. Deléglise, U. B. Hoff, M. Brune, J.-M. Raimond, and S. Haroche, Nature 446, 297 (2007).
- S. Reick, K. Mølmer, W. Alt, M. Eckstein, T. Kampschulte, L. Kong, R. Reimann, A. Thobe, A. Widera, and D. Meschede, J. Opt. Soc. Am. B 27, A 152 (2010)

#### Masahito Ueda *(The University of Tokyo, Japan)*

##### Universality in Few-Body Physics

The three-body parameter, which governs the lifetime of ultracold atomic gases, has long been believed to be a random parameter varying from one atomic species to another and from one Feshbach resoance to another of the same species. Surprisingly, recent experiments have found that the three-body parameter has a universal value when measured in units of the van der Waals length, regardless of the atomic species and the location of the Feshbach resonance. In this talk, I will discuss the underlying physics of this universality and its implication to many-body physics.

#### Jason Twamley* (Macquarie University, Australia)*

##### Connecting up a quantum internet - building optical networks of superconducting quantum devices

Superconducting devices have developed rapidly and are able to execute detailed coherent control over multi-partite quantum information locally on a chip. To build up more global quantum information networks with superconducting devices it is vital to have a device that interfaces the quantum information held in superconducting devices with optical quantum networks. We describe a theoretical proposal for the design of such an interface and describe how it can implement coherent quantum transport between two distant superconducting devices and is robust against noise.

#### Leticia Tarruell* (ICFO-The Institute of Photonic Sciences, Spain)*

##### Exploring synthetic quantum materials with ultracold fermions in a tunable-geometry optical lattice (Slides)

Ultracold Fermi gases in optical lattices have emerged as a versatile tool to study condensed matter model systems. They give access to the simulation of traditional condensed-matter problems in a more controlled setting and also to the realization of extreme parameter regimes which are not accessible in solid-state samples. In my talk I will present experiments where an ultracold Fermi gas trapped in an optical lattice of tunable geometry is used to explore both aspects.

By loading non-interacting atoms into a honeycomb lattice, we realize artificial graphene and observe the presence of two Dirac points in the band structure [1]. The flexibility of our experimental approach allows us to adjust the properties of the Dirac points at will, changing the effective mass of the Dirac fermions, moving the Dirac points inside the Brillouin zone and observing the topological transition associated to their merging.

Preparing instead a repulsively interacting gas of atoms in two different internal states we implement the Fermi-Hubbard model and aim at simulating quantum magnetism in this system. In particular, we explore experimentally how certain crystal geometries favor the emergence of short-range magnetic order, and directly probe the nearest-neighbor spin correlations of the system [2]. In a dimerized lattice, the correlations manifest as an excess number of singlets as compared to triplets, whereas in an anisotropic simple cubic lattice we observe the appearance of antiferromagnetic correlations along one spatial axis.

[1] L. Tarruell, D. Greif, T. Uehlinger, G. Jotzu and T. Esslinger, “Creating, moving and merging Dirac points with a Fermi gas in a tunable honeycomb lattice”, Nature **483**, 302–305 (2012).

[2] D. Greif, T. Uehlinger, G. Jotzu, L. Tarruell and T. Esslinger, “Short-range quantum magnetism of ultracold fermions in an optical lattice”, Science **340**, 1307-1310 (2013).

#### Joseph Fitzsimons *(Center for Quantum Technologies, Singapore)*

##### Quantum correlations which imply causation

In ordinary, non-relativistic, quantum physics, time enters only as a parameter and not as an observable: a state of a physical system is specified at a given time and then evolved according to the prescribed dynamics. While the state can, and usually does, extend across all space, it is only defined at one instant of time, in conflict with special relativity where space and time are treated on an equal footing.

The quantum density matrix can be expressed in a manner which depends only on measurement expectation values, rather than quantum states, and so may be naturally generalized to incorporate non-simultaneous measurements. In this talk, I will explore the consequences of such a generalization. Such pseudo-density matrices have many of the same properties as standard density matrices, but are not constrained to be positive semi-definite. This motivates the definition of a measure of causality that discriminates between spacelike and timelike correlations. This measure satisfies several important properties, such as monotonicity under local operations. Finally, I will report on the results of two qubit NMR experiments that illustrate how a temporal pseudo-density matrix approaches a genuinely allowed density matrix as the amount of decoherence is increased between two consecutive measurements.

#### Tim Byrnes *(National Institute of Informatics, Japan)*

##### Spin coherent states for quantum information (Slides)

Alternative models of quantum computation that go beyond the standard qubit formalism offer potentially new approaches to building a large scale quantum information processing device. Past examples that have gained significant attention are continuous variables, measurement based, topological, and holonomic quantum computation.

Here we discuss a method of using spin coherent states, particularly realized in two-component BECs, for quantum information processing. We construct a general framework for quantum algorithms to be executed using spin coherent states. We illustrate the scheme by an application to quantum algorithms and discuss the effects of decoherence induced by the large number of particles in the BEC. We also discuss a new quantum teleportation protocol that allows for the transfer of a spin coherent states between two parties, assisted by entanglement. In the protocol, two macroscopic spin state are entangled, and an initially unknown spin coherent state is transferred to a distant location. Unlike standard quantum teleportation where a single qubit is transferred, a macroscopic ensemble of spins is teleported in our scheme. By the use of a special class of entangled states, it is possible to avoid the detrimental effects of decoherence n such macroscopic state on the protocol.

[1] Tim Byrnes, Kai Wen, Yoshihisa Yamamoto, Phys. Rev A 85, 040306 (R)

[2] Alexey Pyrkov and Tim Byrnes, arxiv 1305.2479

#### Michael Köhl *(University of Bonn, Germany)*

##### Spin dynamics in two-dimensional Fermi gases

Harnessing spins as carriers for information has emerged as an elegant extension to the transport of electrical charges. The coherence of such spin transport in spintronic circuits is determined by the lifetime of spin excitations and by spin diffusion. Fermionic quantum gases are a unique system to study the fundamentals of spin transport from first principles since interactions can be precisely tailored and the dynamics is on time scales which are directly observable. In particular at unitarity, spin transport is dictated by diffusion and is expected to reach a universal, quantum-limited diffusivity on the order of ħ/m. Here, we study the non-equilibrium dynamics of a two-dimensional Fermi gas following a quench into a metastable, transversely polarized spin state. Using the spin-echo technique, we measure the yet lowest (in any system) transverse spin diffusion constant. For weak interactions, we observe a coherent collective transverse spin-wave mode that exhibits mode softening when approaching the strongly interacting regime.

#### Haruka Maeda *(Aoyama Gakuin University, Japan)*

##### Coherent control of Rydberg atoms (Slides)

Rydberg atom, in which one of the outer-most valence electron(s) is excited to a state with large principal quantum number n, has quite unique properties due mainly to its huge atomic size. As binding energy of valence electron is proportional to 1/n^{2}, Rydberg electron is extremely sensitive to external fields. Furthermore, energy separation between n and n+1 Rydberg states (µ1/n^{3}) is very small, resulting in resonance frequencies of Rydberg atom in microwave (MW) or RF regime. Together with further unique properties of Rydberg atom such as, for example, long radiative lifetime (µ n^{3} ), huge electric dipole moment between adjacent Rydberg states (µ n^{2} ), long Kepler orbit time (µ n^{3}), Rydberg atom offers fascinating playground of studying nonlinear phenomena coherently induced in multilevel ladder system by an irradiation of near resonant field. In my talk I will present recent experimental results on multiphoton ionization of Rydberg atoms, non-dispersing Rydberg wave-packet creation, and population transfer of Rydberg atoms. In either case, multi-level coupling of Rydberg states by near resonant microwave fields plays a crucial role to understand thesenonlinear phenomena.

#### Alexander Szameit *(Friedrich-Schiller University Jena, Germany)*

##### Photonic Graphene: The physics of honeycomb waveguide lattices

Graphene – a single monolayer of Carbon atoms arranged in honeycomb geometry – offers a plethora of exciting phenomena. Importantly, most of those arise due to the underlying topology of the lattice and do not depend on the electronic nature of graphene. In contrast, any structure exhibiting the unique honeycomb topology should possess similar features.

In my presentation, I will review our recent activities on light evolution in evanescently coupled waveguide lattices in a honeycomb arrangement. In such “photonic graphene” we are able to analyse theoretically and experimentally various phenomena, such as edge states, ultra-strong pseudo-magnetic fields, optical tachyons, and even photonic topological insulators – a “superconductor for light”. Our research opens a gate for a deep understanding of the graphene topology that can goes beyond the electronic system.

**Figure:** Left – a microscope image of the front facet of an optical waveguide array in honeycomb geometry. Right – the dispersion relation of the optical system is equivalent to the electronic system, and also exhibits in particular the 6 singular vertices between the two tight-binding bands.

#### Corinna Kollath *(University of Geneva, Switzerland)*

##### Effects of dissipation in strongly correlated ultracold gases

Atomic gases cooled to Nanokelvin temperatures are a new exciting tool to study a broad range of quantum phenomena. In particular, an outstanding and rapid control over the fundamental parameters, such as interaction strength, spin composition, and dimensionality allows to realize and observe many different situations far from equilibrium. Long-standing questions such as the coupling to an environment can be investigated. In my talk, I will address the question of the influence of a coupling to an environment on the system dynamics in bosonic and fermionic optical lattice gases. We find that the environment can cause unconventional relaxation dynamics often described by spatially dependent classical diffusion equations. In bosonic interacting gases a glass-like relaxation can be found. Even more surprising, in fermionic gases we show that local incoherent dissipation can induced long distance correlations starting from an incoherent Mott-insulating state.

#### Kyungwon An *(Seoul National University, Korea)*

##### 3D imaging of cavity vacuum with single atoms (Slides)

Atomic spontaneous emission can be viewed as being stimulated by vacuum fields associated with zero-point energy, as first discussed by P. A. M. Dirac. When an excited atom is placed in a high-Q cavity, it is driven by the cavity vacuum field at its position and emits a photon into the cavity mode. The emission rate is proportional to the vacuum-field intensity. By changing the atomic position and measuring the emission out the cavity, we can then perform 3D imaging of the cavity vacuum that the atom interacts with. For this, we employ a beam of barium atoms. Transverse localization of single atoms is achieved by using a nanohole-array aperture scannable in front of the cavity mode. The transit-time broadening encoded in the atom-cavity detuning curve provides the vacuum field profile along the direction of atomic beam. In this way the 3D profile of the vacuum field in a Fabry-Perot cavity is imaged with a spatial resolution of about 170 nm, which is mostly limited by the nanohole diameter. The rms amplitude of the vacuum field at the antinode is also measured to be 0.92 ± 0.07 V/cm, consistent with the estimate based on the mode volume and zero-point energy conservation. The present work utilizing a single atom as a probe for sub-wavelength imaging demonstrates the utility of nanometer-scale technology in cavity quantum electrodynamics. Particularly, the periodic nanohole array enables precise control of the atom-cavity coupling constant. One application might be phase imprinting of an atomic superposition state into the cavity field for quantum information processing.

Relevant Literature:

Three-dimensional imaging of cavity vacuum with single atoms localized by a nanohole array,

Nature Communications 5, 3441 (2014)

Prescribed nondegenerate high-order modes in an axial-asymmetric high-finesse Fabry–Perot microcavity,

Optics Letters 37, 1457 (2012)

#### Jing Zhang* (Shanxi University, China)*

**Spin-orbit coupled degenerate Fermi gas (Slides)**

We report the first experimental realization of SO coupled degenerate Fermi gas. Evidences of spin-orbit coupling have been obtained from the Raman Rabi oscillation and the spin-dependent momentum distribution asymmetry. We also find that the momentum distribution in helical bases is consistent with topological changes of Fermi surfaces. Recently, we bring the experimental system close to a Feshbach resonance. We report characteristic blue and red shifts in the atomic and molecular responses, respectively. And we demonstrate a dynamic process in which SO coupling can coherently produce s-wave Feshbach molecules from a fully polarized Fermi gas, and can induce a coherent oscillation between Feshbach molecules and spin polarized gas. This progress enables us to study stronger pairing and higher Tc enhanced by SO coupling in resonant interacting Fermi gases and topological insulator and topological superfluid in a more flexible setup in near future.

**References:**

[1] P. Wang, Z. Yu, Z. Fu, J. Miao, L. Huang, S. Chai, H. Zhai, J. Zhang, Phys. Rev. Lett. 109, 095301 (2012)

[2] Z. Fu, L.i Huang, Z. Meng, P. Wang, X-J. Liu, H. Pu, H. Hu, J. Zhang, Phys. Rev. A 87, 053619 (2013).

[3] Z. Fu, P. Wang, L. Huang, Z. Meng, H. Hu, J. Zhang " Optical control of a magnetic Feshbach resonance in ultracold Fermi gases" Phys. Rev. A 88, 041601(R）(2013).

[4] Z. Fu, L.i Huang, Z. Meng, P. Wang, L. Zhang, S. Zhang, H. Zhai, P. Zhang, J. Zhang, "Spin-Orbit Coupling Induced Coherent Production of Feshbach Molecules in a Degenerate Fermi Gas" arXiv:1306.4568.

#### Jürgen Eschner *(Saarland University, Germany)*

##### Single-photon – single-ion interfaces (Slides)

Quantum networks require the conversion between photonic and atomic quantum states. We demonstrate various implementations of controlled interaction between single trapped ions and single photons.

We generate single photons with controlled temporal, spectral, and polarisation properties through a laser-driven spontaneous Raman process [1-3]. The photons have between ~15 ns and ~1 µs duration and are near-Fourier-limited [1,2]. In one experiment, single photons from one ion are transmitted over ~1 m distance to a second single ion, where they are absorbed; individual absorption events are detected employing a quantum-jump heralding scheme [3]. In another experiment, Raman photons are generated from an ion which is initially prepared in a coherent superposition of Zeeman sub-levels. With this method, heralded quantum storage of photon polarisation states, as proposed in [4,5], is experimentally realized [6].

We also demonstrate heralded absorption by a single trapped ion of single photons from a Spontaneous Parametric Down-Conversion (SPDC) source; the entanglement of the SPDC photon pair is manifested in the polarisation correlation between photon absorption and detection of the heralding partner [7,8].

[1] Bandwidth-tunable single-photon source in an ion-trap quantum network,

M. Almendros et al., Phys. Rev. Lett. **103**, 213601 (2009).

[2] A high-rate source for single photons in a pure quantum state,

C. Kurz et al., New J. Phys. **15**, 055005 (2013).

[3] Heralded photonic interaction between distant single ions,

M. Schug et al., Phys. Rev. Lett. **110**, 213603 (2013).

4] Heralded mapping of photonic entanglement into single atoms in free space…

N. Sangouard et al., New J. Phys. **15**, 085004 (2013).

[5] Single calcium-40 ion as quantum memory for photon polarization: a case study

P. Müller, J. Eschner, Appl. Phys. B, published online; arxiv:1309.7863

[6] High-fidelity heralded photon-to-atom quantum state transfer

C. Kurz et al., arxiv:1312.5995.

[7] Heralded single-photon absorption by a single atom,

N. Piro et al., Nature Physics **7**, 17 (2011).

[8] Photon entanglement detection by a single atom,

J. Huwer et al., New J. Phys. **15**, 025033 (2013).

## Participants

##### Bess Fang, Laboratoire Charles Fabry, Institut d'Optique, France

Quench-induced breathing mode of one-dimensional Bose gases (Slides)

##### Thanh Phuc Nguyen, The University of Tokyo, Japan

Emergent energy gap of quasi-Nambu-Goldstone modes and their propagations in spinor Bose-Einstein condensates

##### Matthew Davis, University of Queensland, Australia

Emergence of order from turbulence in an isolated planar superfluid (Slides)

##### Daniel Burgarth, Aberystwyth University, United Kingdom

Quantum Computing in Plato's Cave

##### Samuel Mugel, University of Southampton, United Kingdom

Topological Bound States generated by Cold Atoms performing a Quantum Walk

##### Tomasz Sowinski, Institute of Physics of the Polish Academy of Sciences, Poland

Spontaneous breaking of the time-reversal symmetry in optical lattices

##### Bianca Sawyer, University of Otago, New Zealand

Driven pseudospin dynamics in a gradient field

##### Adam Zaman Chaudhry, National University of Singapore, Singapore

Amplification of system-bath correlation effects in an open many-body system

##### Meng-Jung Lee, National Tsing-Hua University, Taiwan

Observation of spinor-slow-light oscillation

##### Kazuto Noda, NTT Basic Research Laboratories, NTT Corp., Japan

Ferromagnetism in optical multilayered-Lieb lattices

##### Sammy Ragy, University of Nottingham, United Kingdom

Simultaneous parameter estimation on qubits

##### Gabriele De Chiara, Queen's University of Belfast, United Kingdom

Entanglement spectrum dynamics in critical systems (Slides)

##### Matthew Jones, University of Nottingham, United Kingdom

Ultracold Bose-Fermi Mixture of Lithium and Caesium

##### Joseph Cotter, University of Vienna, Austria

Decoherence spectroscopy of large, complex molecules

##### Yue Ban, Shanghai University, China

Spin Control in Quantum Dots By Shortcut To Adiabaticity

##### Antonio Negretti, University of Hamburg, Germany

Quantum simulation with ultracold atoms and ions

##### Robert Spreeuw, University of Amsterdam, Netherlands

Lattices of magnetic micro traps as an experimental platform for quantum control

##### Eoin Butler, Imperial College London, United Kingdom

Interferometry with Bose-Einstein Condensates on an Atom Chip - A search for short-range forces

##### Marta Abad Garcia, INO-CNR BEC Center and University of Trento, Italy

Coherently coupled two-component Bose gases

##### Si Hui Tan, Singapore University of Technology and Design, Singapore

Sampling Immanants with Interferometers with Single-Photon Inputs

##### Margherita Zuppardo, Nanyang Technological University, Singapore

Different ways of distributing quantum entanglement

##### Axel Pelster, Technical University of Kaiserslautern, Germany

Tuning the Quantum Phase Transition of Bosons in Optical Lattices via Periodic Modulation of s-Wave Scattering Length

##### Lianghui Huang, Shanxi University, China

Spin-orbit coupled degenerate Fermi gas

##### Edina Szirmai, Budapest University of Technology and Economics, Hungary

Stability of spin liquid phases of alkaline earth atoms at finite temperature (Slides)

##### Maria Schuld, University of KwaZulu-Natal, South Africa

Quantum Neural Networks - prospects of a growing research field

##### Jingbo Wang, The University of Western Australia, Australia

Quantum simulation via quantum walks with specifically designed defects and disorder

##### Malte Christopher Tichy, University of Aarhus, Denmark

Generation and observation of non-ideal composite bosons

##### Gentaro Watanabe, Asia Pacific Center for Theoretical Physics (APCTP), Korea

Dissipative preparation of squeezed states with ultracold atomic gases (Slides)

##### Akshata Shenoy H., Indian Institute of Science, Bangalore, India

Device-independent quantum cryptography using graph states

##### Bernhard Rauer, Vienna University of Technology, Austria

Relaxation Dynamics of Isolated Quantum Many-Body Systems

##### Stefan Putz, Vienna Center for Quantum Science and Technology (VCQ), Austria

Inducing Coherent Oscillations in the Strong Coupling Regime of Cavity QED

##### Yui Kubo, CEA Saclay, France

Towards a spin-ensemble quantum memory for superconducting qubits (Slides)

##### Kieran Higgins, University of Oxford, United Kingdom

Superabsorption of light via quantum engineering

##### Yuichiro Matsuzaki, NTT Basic Research Laboratories, NTT Corp., Japan

Vacuum Rabi Oscillation Between a Superconducting Flux Qubit and NV Centers in Diamond: a theoretical analysis

##### Elisa Fratini, Abdus Salam International Centre for Theoretical Physics, Italy

Resonant Bose-Fermi mixtures: a T-matrix and Quantum Monte Carlo Study

##### Katarzyna Macieszczak, University of Nottingham, United Kingdom

Efficient iterative algorithm to compute maximum quantum Fisher Information

##### Ippei Danshita, Yukawa Institute for Theoretical Physics, Kyoto University, Japan

Bose-Bose mixtures in optical lattices: quantum tricriticality and a bright-like dark soliton

##### Marcin Płodzień, Jagiellonian University, Poland

Matter-wave interference versus spontaneous pattern formation in spinor Bose-Einstein condensates

##### Pinja Haikka, Aarhus University, Denmark

Continuously montiored Landau-Zener model

##### Xi Chen, Shanghai University, China

Shortcuts to adiabatic passage for population transfer in two and three level systems

##### Uwe R. Fischer, Seoul National University

Ultrafast quantum random access memory utilizing single Rydberg atoms in a Bose-Einstein condensate

(Related paper 1, 2)

##### Adolfo del Campo, Los Alamos National Laboratory, USA

Shortcuts to adiabaticity in many-body systems

##### Junki Kim, Seoul National University, Korea

Coherently pumped cavity-QED microlaser

##### Miguel Angel Garcia March, Universitat de Barcelona, Spain

Spatial localization and quantum correlations in small mixtures of ultracold bosons in very different interacting regimes

##### Lee O'Riordan, OIST, Japan

Coherent transport by adiabatic passage on atom chips

##### Angela White, OIST, Japan

All things topological: stirring and winding up Bose-Einstein Condensates

##### Albert Benseny Cases, OIST, Japan

Hybrid systems of ions and electric-dipolar condensates

##### Mark Daly, OIST, Japan

Fluorescent excitation of nanofibre higher order modes, OIST, Japan (Slides)

##### Ciaran Phelan, OIST, Japan

Cold atom trapping with a nanostructured optical nanofiber

##### Ravi Kumar, OIST, Japan

Sensing cold atoms with a hot sensor

##### Nitesh Dhasmana, OIST, Japan

Four-wave mixing in microsphere resonator

##### Jérémie Gillet, OIST, Japan

Tunneling, self-trapping and manipulation of higher modes of a BEC in a double well (Slides)

##### Kieran Deasy, OIST, Japan

Fluorescent excitation of nanofibre higher order modes

##### Tara Hennessy, OIST, Japan

Few-mode tapered fibers for detecting and trapping neutral atoms

##### Yongping Zhang, OIST, Japan

Gap solitons in Bose-Einstein condensate with spin-orbit coupled optical lattice

##### Chandrashekar Madaiah, OIST, Japan

Quantum percolation of a qubit on a directed two-dimensional lattice with random disconnections

##### Vandna Gokhroo, OIST, Japan

Probing 2-photon absorption in cold atoms using an optical nanofiber