2017 Spring Schedule

*Unless otherwise noted, all events will take place in Jefferson 250*

Student presentation begins at 4:00 PM

Refreshments are served from 4:10-4:30 PM

Guest presentation begins at 4:30 PM

**Wednesday, December 13th – Prof. Andrea Cavalleri (Max Planck Institute for the Structure and Dynamics of Matter, Hamburg GERMANY Department of Physics, University of Oxford)**

**Nonlinear THz optics as probe of quantum solids**

In this lecture, I will discuss how coherent electromagnetic radiation at infrared and TeraHertz frequencies can be used to collective excitations like phonons in solids. I will emphasize experiments in which hidden features the superconducting order parameter can be revealed. I will also discuss advances in the nonlinear response of phonons, which I will show can be used as a probe of the interatomic potential of a solid.

**Wednesday, November 29th – Dr. Pierre Pillet (Laboratoire Aimé Cotton, CNRS, Univ Paris-Sud, ENS Paris-Saclay)**

**Interplay between two-, few- and many-body effects in a dense, cold and disordered gases in strong dipole-dipole coupling**

Dipole-dipole long-range interactions between two atoms in dense and cold atomic media play a crucial role in many configurations by considering ground state atoms as well as highly-excited Rydberg atoms. They may alter the coherent scattering of light by a dense and cold atomic sample. They open also many opportunities for studying few-body and many-body physics, and hopefully for simulating many different quantum systems. A cold, disordered and dense cesium Rydberg gas in Förster resonant configurations is an interesting example of out-of-equilibrium quantum system. The atoms are prepared in a state, np, exchanging internal energy by a resonant way +→+(+1) (the resonance is obtained by Stark shift of the p level). The reaction due dipole-dipole interaction leads to a very efficient transfer of population from the p level to the s ones. The Förster coupling offer the possibility to isolate few-body effects from two-body ones and to characterize their features. A saturation regime can be reached, characterized by an amazing behavior corresponding to the “thermalization” of the atomic sample, meaning an equal-distribution of the populations of the relevant levels of the resonant reaction. The dynamics of the thermalization seems to be the result of few-body effects. The interplay between two-, few- and many-body regime in dipole coupling will be discussed, as so well as the role of the diffusion scattering of the products of the reaction.

**Wednesday, November 15 – Dr. Tongcang Li, Purdue University**

website: https://sites.google.com/site/litongcang/

**Levitated spin-optomechanics**

Optomechanical systems, such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) and atomic force microscopes, are very sensitive devices. Among different optomechanical systems, an optically levitated nanoparticle in vacuum can have a particularly high quality factor. In this talk, I will discuss how to couple the mechanical motion of an optically levitated nanoparticle to photon spins, electron spins, and the spin angular momentum of quantum vacuum fluctuations for sensing, quantum information science, and macroscopic quantum mechanics. Recently, we optically levitated a nanodiamond and demonstrated electron spin control of its built-in nitrogen-vacancy (NV) centers in vacuum. We have also driven a nanoparticle to rotate beyond 1GHz with a circularly polarized laser beam, and observed the torsional vibration of a nanoparticle with a linearly polarized laser beam. Based on our experimental results, we propose to achieve strong coupling between an NV electron spin and the torsional vibration of a levitated nanodiamond with a uniform magnetic field. We also propose to use our system to detect the Casimir torque due to angular momentum of quantum vacuum fluctuations, which has not been observed to date. At the end of the talk, I will briefly describe my other works in quantum optics.

**Wednesday, November 1 – Dr. Ronnie Kosloff, Hebrew University of Jerusalem**

website: https://scholars.huji.ac.il/ronniekosloff

**Thermodynamics of quantum devices**

Quantum thermodynamics addresses the emergence of thermodynamical laws from quantum me- chanics. The viewpoint advocated is based on the intimate connection of quantum thermodynamics with the theory of open quantum systems. Quantum mechanics inserts dynamics into thermody- namics giving a sound foundation to finite-time-thermodynamics. The emergence of the 0-law I-law II-law and III-law of thermodynamics from quantum considerations will be presented through exam- ples. I will show that the 3-level laser is equivalent to Carnot engine. I will reverse the engine and obtain a quantum refrigerator. Different models of quantum refrigerators and their optimization will be discussed. A heat-driven refrigerator (absorption refrigerator) is compared to a power-driven refrigerator related to laser cooling. This will lead to a dynamical version of the III-law of thermo- dynamics limiting the rate of cooling when the absolute zero is approached. The thermodynamically equivalence of quantum engines in the quantum limit of small action will be discussed. I will ad- dress the question why we find heat exchangers and flywheels in quantum engines. I will present a molecular model of a heat rectifier and a heat pump in a non-Markovian and strong coupling regime. Finely the question of quantum supremacy in heat devices will be adressed.

**Wednesday, October 18 – Dr. Xiaodong Xu, University of Washington
**

website: http://depts.washington.edu/xulab/

**Monolayer Magnets**

Since the discovery of graphene, the family of two-dimensional (2D) materials has grown to encompass a broad range of electronic properties. However, until recently 2D crystals with intrinsic magnetism were still lacking. Such crystals would enable new ways to study 2D magnetism by harnessing the unique features of atomically-thin materials, such as electrical control for magnetoelectronics and van der Waals engineering for novel interface phenomena. In this talk, I will describe our recent magneto-optical spectroscopy experiments on van der Waals magnets, chromium(III) iodide CrI3. I will first demonstrate the existence of isolated monolayer semiconductor with intrinsic Ising ferromagnetism. I will then show the layer number-dependent magnetic phases. The magnetic ground state evolves from being ferromagnetic in a monolayer, to antiferromagnetic in a bilayer, and back to ferromagnetic in a trilayer and thin bulk. Lastly, I will discuss the emerging spin phenomena in monolayer WSe2/CrI3 ferromagnetic semiconductor heterostructures, including ferromagnetic control of valley pseudospin in WSe2 via large magnetic exchange field, and optical analog of giant magnetoresistance effect.

**Wednesday, May 3 – Dr. Hannes Bernien, Harvard University
**

website: http://bernien.weebly.com/

**Quantum many-body dynamics of strongly interacting atom arrays**

The realization of large-scale controlled quantum systems is an exciting frontier in modern physical science. In this talk, I will introduce a new platform based on cold atoms in arrays of optical tweezers. We use atom-by-atom assembly to deterministically prepare arrays of individually controlled cold atoms. A measurement and feedback procedure eliminates the entropy associated with the probabilistic trap loading and results in defect-free arrays of over 60 atoms. Strong controllable interactions between these atoms are introduced by exciting them to Rydberg states. The resulting Ising-type interactions lead to entanglement and non-trivial spatial correlations across the array. In particular, we explore adiabatic transitions into crystalline states and study quantum dynamics of this strongly correlated system in the vicinity of a phase transition. Prospects for studying entanglement dynamics in many-body systems and the implementation of quantum algorithms will be discussed.

**Wednesday, April 19 – Norman Yao, UC Berkeley
**

website: http://physics.berkeley.edu/people/faculty/norman-yao

**One Dimensional Time-Translation Symmetry Breaking: From Power-laws to Classical Dynamical Systems
**

Non-equilibrium systems can exhibit phenomena fundamentally richer than their static counterparts. For example, certain phases of matter that are provably forbidden in equilibrium, such as quantum time crystals, have found new life in out-of-equilibrium systems. In this talk, I will begin by summarizing recent advances, which predicted the spontaneous breaking of time translation symmetry in periodically driven quantum systems and culminated in the experimental observation of time crystals in two disparate systems. The resulting time crystal exhibits collective oscillations – arising from many-body synchronization – that are quantized to an integer multiple of the drive period. I will then describe two new examples of “surprising” time-translation symmetry breaking in one dimensional systems. The first will focus on long-range pre-thermal time crystals, while the second will address the possibility of classical time crystals.

**Wednesday, April 5 – Chris Monroe, JQI and University of Maryland
**

website: http://iontrap.umd.edu/

**Building a Quantum Computer, Atom by Atom
**

Laser-cooled and trapped atomic ions are standards for quantum information science, acting as qubits with unsurpassed levels of quantum coherence while also allowing near-perfect measurement. When qubit state-dependent optical forces are applied to a collection of ions, their Coulomb interaction is modulated in a way that allows entanglement operations that form the basis of a quantum computer. Similar forces allow the simulation of quantum magnetic interactions, and recent experiments have implemented tunable long-range interacting spin models with up to 40 trapped ions. Scaling to even larger numbers can be accomplished by coupling trapped ion qubits to optical photons, where entanglement can be formed over remote distances for applications in quantum communication, quantum teleportation, and distributed quantum computation. By employing such a modular and reconfigurable architecture, it should be possible to scale up ion trap quantum networks to useful dimensions, for future quantum applications that are impossible using classical processors.

**Wednesday, March 22 – Randall Hulet, Rice University
**

website: http://atomcool.rice.edu/

**Pairing of Spin Polarized Fermi Gases
**

Ultracold atomic gases are versatile platforms for realizing novel many-body states of matter by virtue of the ability to tune parameters such as interaction, density, dimensionality, and spin-polarization. I will describe experiments that have produced phase diagrams of spin-polarized Fermi gasses in 1D, 3D, and in the 1D-3D dimensional crossover. I will conclude with our progress to create the holy grail of this research, which is the observation of the “elusive” FFLO superfluid state, a state that exhibits coexisting magnetic and superconducting order.

**Wednesday, March 8 – Ortwin Hess, Imperial College London
**

website: https://www.imperial.ac.uk/people/o.hess

**Controlled Single-Molecule Strong Coupling and Stopped-Light Lasing in Nanoplasmonic Cavities
**

Recent progress in nanophotonics and metamaterials physics is now allowing us to ‘look inside the wavelength’ and exploit active nano-plasmonics and metamaterials as a new route to quantum many-body optics on the nanoscale [1,2]. At the same time, lasers have become smaller and smaller, reaching with the demonstration of plasmonic nanolasing, scales much smaller than the wavelength of the light they emit [3,4]. Here we discuss recent progress in the study of quantum emitters and quantum gain in nanoplasmonic systems and deliberate on approaches. We combine classical and quantum many-body theory and simulation to describe and model the spatio-temporal dynamics of the optical near field and plasmon polaritons coupled with quantum emitters in nano- plasmonic cavities. We reveal the mechanisms that have allowed us to experimentally reach the strong-coupling regime at room temperature and in ambient conditions [5]. Moreover, it will be demonstrated that applying the nanoplasmonic stopped-light lasing principle to surface- plasmon polaritons (SPP) facilitates trapped/condensed non-equilibrium surface-plasmon polaritons at stopped-light singularities, providing an entry point to SPP-condensation.

[1] O. Hess et al. Nature Materials 11, 573 (2012).

[2] O. Hess et al., Science 339, 654 (2013).

[3] T. Pickering, et al., Nature Communications 5, 4971 (2014).

[4]S. Wuestner, T. Pickering, J. M. Hamm, A. F. Page, A. Pusch and O. Hess, Faraday Discuss. 178, 307 (2015).

[5] R. Chikkaraddy, B. de Nijs, F. Benz, S. J. Barrow, O. A. Sherman, E. Rosta, A. Demetriadou, P. Fox, O. Hess and J.J. Baumberg, Nature 535, 127(2016).

**Wednesday, November 30 - Immanuel Bloch, Max Planck Institute of Quantum Optics, Garching; Ludwig-Maximillians University, Munich
**

website: https://www.quantum-munich.de/people/person-details/pers/1/

**Probing Hidden Non-local Antiferromagnetism & Many-Body Localisation Using Ultracold Atoms
**

Recent experiments with quantum gas microscopes allow for an unprecedented view and control of quantum matter in new parameter regimes and with new probes. In our fermionic quantum gas microscope, we can detect both charge and spin degrees of freedom simultaneously, thereby gaining maximum information about undoped or strongly doped fermionic Hubbard systems. The doped 1D systems are characterised by a hidden non-local antiferromagnetic (AFM) order that can be revealed using non-local string correlators, very similar to the non-local topological order in Spin-1 Haldane chains. The hidden AFM order probed in our experiments is the foundation of spin-charge separation in one-dimensional fermionic systems.

Finally, I will discuss our recent experiments on novel many-body localised (MBL) states of matter that challenge our understanding of the connection between statistical physics and quantum mechanics at a fundamental level. I will also discuss very recent experiments, in which he have observed evidence for Griffith type anomalous slow transport on the ergodic side of the MBL transitions.

**Wednesday, November 2 - Mete Atatüre, University of Cambridge
**

website: http://www.phy.cam.ac.uk/directory/ataturem

**Solid-State Spin-Photon Interfaces: Old Friends and New
**

Optically active spins confined in solids, such as semiconductors or diamond, are interesting and rich physical systems for quantum science and its applications. Their inherently mesoscopic nature leads to a multitude of dynamics within the solid state environment of spins, charges, vibrations and light. While the quantum optics provides a toolbox for advanced spectroscopic investigations for these interaction mechanisms, it also offers solution possibilities for their detrimental effects for the realisation of operational quantum devices. Implementing a high level of control on these constituents and their interactions with each other creates exciting opportunities for realizing stationary and flying qubits within the context of spin-based quantum information science. In this talk, I will provide a snapshot of the progress and challenges for interconnected solid-state spins, as well as first steps towards hybrid quantum devices involving emergent materials.

**Wednesday, October 19 - Ferdinand Schmidt-Kaler, Johannes Gutenberg—University of Mainz
**

website: http://www.quantenbit.de/publications/

**Quantum optics and quantum information with trapped ions
**

The quantum states of ions are perfectly controlled, and may be used for fundamental research in quantum physics, as highlighted by the Nobel Prize given to Dave Wineland in 2012. In this talk, I will highlight the advantages of trapped ions for quantum information processing, taking advantage of modern trap technologies to pave a way for scalability. The laser-ion interactions allow for high fidelity quantum gate operations, while the application of well-suited trap control voltages realizes ion shuttles and the reconfiguration of the ion quantum register. Alternatively, one may employ Rydberg excitation of trapped ions to allow for long-range interactions and quantum gate operation.

**Wednesday, September 21 – Jelena Vuckovic, Stanford**

website: http://web.stanford.edu/~jela/

**Quantum Nanophotonics
**

Nanophotonic structures that localize photons in sub-wavelength volumes are possible today thanks to modern nanofabrication and optical design techniques. Such structures enable studies of new regimes of light-matter interaction, quantum and nonlinear optics, and new applications in computing, communications, and sensing. I will review our recent work on the traditional quantum nanophotonics platform based on InAs quantum dots inside GaAs photonic crystal cavities [1-3], as well as our progress on alternative material systems diamond and silicon carbide [4], which could potentially bring the described experiments to room temperature and facilitate scaling to large networks of resonators and emitters. Finally, the use of inverse design nanophotonic methods [5], that can efficiently perform physics-guided search through the full parameter space, leads optical devices with properties superior to state of the art, including smaller footprints, better field localization, and novel functionalities.

[1] Optica, vol. 3, 931-936 (2016)

[2] Nature Photonics,vol. 10, pp. 163-166 (2016)

[3] Physical Review Letters, vol. 114, 233601 (2015)

[4] Nano Letters, vol. 16 (1), pp. 212-217 (2016)

[5] Nature Photonics 9, 374–377 (2015)

**Wednesday, September 7 – Franco Nori, RIKEN, Saitama, Japan; University of Michigan, Ann Arbor, MI
**

website: http://www-personal.umich.edu/~nori/ http://dml.riken.jp/

**Extraordinary properties of light: Evanescent waves and quantum spin Hall effect
**

Maxwell’s equations ultimately describe properties of light, from classical electromagnetism to quantum and relativistic aspects. The latter ones result in remarkable geometric and topological phenomena related to spin-1 massless nature of photons. By analyzing fundamental spin properties of Maxwell waves, we show that free-space light exhibits an intrinsic quantum spin Hall effect—surface modes with strong spin-momentum locking. These modes are evanescent waves that form, for example, surface plasmon-polaritons at vacuum-metal interfaces. Our findings illuminate the unusual transverse spin in evanescent waves and explain recent experiments that have demonstrated the transverse spin-direction locking in the excitation of surface optical modes.

Optical systems combining balanced loss and gain provide a unique platform to implement classical analogues of quantum systems described by non-Hermitian parity–time (PT)-symmetric Hamiltonians. Such systems can be used to create synthetic materials with properties that cannot be attained in materials having only loss or only gain. We report PT-symmetry breaking in coupled optical resonators and observe non-reciprocity in the PT-symmetry-breaking phase due to strong field localization, which significantly enhances nonlinearity. Our results could lead to a new generation of synthetic optical systems enabling on-chip manipulation and control of light propagation.

References:

K.Y. Bliokh, D. Smirnova, F. Nori, Quantum spin Hall effect of light, Science 348, 1448-1451 (2015).

K. Y. Bliokh, A. Y. Bekshaev, F. Nori, Extraordinary momentum and spin in evanescent waves, Nature Communications 5, 3300 (2014).

B. Peng, et al., Parity-time-symmetric whispering-gallery microcavities, Nature Physics 10, 394-398 (2014).