Recent analytical and simulation results on electron acceleration in the bubble regime will be presented. The influence of the effective Gamma-factor of the bubble tail on the trapping process is investigated. The analytically predicted scalings from the similarity theory are compared with the numerical parametric studies.

Quantum dots in photonic crystal nanocavities are interesting both as a testbed for fundamental cavity quantum electrodynamics (QED) experiments, as well as a platform for classical and quantum information processing. In addition to providing a scalable, on-chip, semiconductor platform, this system also enables very large dipole-field interaction strengths, as a result of the field localization inside of sub-cubic wavelength volumes (vacuum Rabi frequency is in the range of 10's of GHz).

We have probed a strongly coupled quantum dot-cavity system coherently, and have demonstrated effects including photon blockade and photon induced tunneling, as well as controlled amplitude and phase modulation between two optical beams at a single photon level. We have also performed resonant spectroscopy and fast electrical control of the quantum dot strongly coupled to a cavity, and combined cavity QED platform with nonlinear frequency conversion.

These demonstrations could be employed to build novel devices, such electro-optic modulators, switches, and lasers with superior performance relative to state of the art devices, and lie at the core of a number of proposals for quantum information processing. For example, I will describe our work on electro-optic modulator controlled with sub-fJ energy, and a laser with threshold current below 100nA - the lowest threshold ever demonstrated in an electrically pumped semiconductor laser.

Entanglement between stationary systems at remote locations is a key resource for quantum networks. We report on the experimental generation of remote entanglement between a single atom inside an optical cavity and a Bose-Einstein condensate (BEC). To produce this, a single photon is created in the atom-cavity system, thereby generating atom-photon entanglement. The photon is transported to the BEC and converted into a collective excitation in the BEC, thus establishing matter-matter entanglement. After a variable delay, this entanglement is converted into photon-photon entanglement. The matter-matter entanglement lifetime of 0.1 ms exceeds the photon duration by two orders of magnitude. The total fidelity of all concatenated operations is 95%. This hybrid system opens up promising perspectives in the field of quantum information.

In this talk I will discuss a recent proposal to prepare and verify spatial quantum superpositions of a nanometer sized object separated by distances of the order of its size. This method merges techniques and insights from cavity quantum optomechanics and matter wave interferometry. An analysis and simulation of the experiment as well as an operational parameter regime will be given by taking into account standard sources of decoherence using present day and planned technology. Finally, I will discuss the unprecedented bounds that this proposed experiment provides to objective collapse models of the wave function.

Precision spectroscopy on atomic hydrogen along with hydrogen's calculable atomic structure have been fueling the development and testing of quantum electro-dynamics (QED) and have lead to the precise determination of the Rydberg constant and the proton and deuteron charge radii.

In particular, the 1S-2S transition with its narrow natural line width of only 1.3 Hz has been measured with great accuracy. These measurements have been used to set limits on a possible variation of fundamental constants and violation of Lorentz boost invariance. It promises to test the charge conjugation/parity/time reversal (CPT) theorem by comparison with the same transition in antihydrogen.

Here, we report on recent results obtained from 1S-2S spectroscopy and give an improved absolute frequency value.

Electron accelerators play a dominant role in basic science as well as in medical or biological applications. However, their size poses a general limitation of their applicability. Laser-plasma acceleration provides a mean of shrinking the size large accelerators and shorten significantly the electron bunch duration. We characterized a laser-driven accelerator in unprecedented detail by observing the accelerating plasma wave and the electron bunch sitting in the plasma at the same time. This way we shoot a film of the acceleration process showing its evolution and measuring the few-fs duration of the electron bunches. The results deliver valuable information that help in deeper understanding and further development of laser-plasma accelerators.

A Bose-Einstein condensate coupled to an optical cavity shows the Dicke quantum phase transition in an open system. The superradiant phase emerges from a broken symmetry and has the character of a supersolid. I will report on experiments characterizing the supersolid phase, the spontaneous breaking of symmetry and the soft mode when approaching the critical point.I will further report on a novel scheme to highly locally probe spin fluctuations in a two-component Fermi gas.

KBBF family crystals, ABe₂BO₃F₂ (A=K, Rb, Cs), are the only type of crystals that can generate deep-UV laser light by direct harmonic generations. The talk starts with briefly introduction of the historical background of the discovery of the borate nonlinear optical (NLO) crystals, followed by the description of the growth, structure, basic properties of the KBBF family crystals. Focuses will be given to the recent progresses on the generation of deep-UV lights, e.g. 120mW at 177.3nm and 1.2W at 200nm. Examples of applications of such deep UV light will be discussed at the end of the talk; which includes: super-high resolution of photoemission spectrometers, photon-electronic emission microscope, etc. 

Attempts to perform quantum computation and generate entanglement typically rely on isolating the system from the environment and reach the desired state trough controlled unitary dynamics. In contrast an alternative approach was proposed, which exploits dissipation to generate entanglement and realize quantum computation as the steady state of the dissipative dynamics. Whether this alternative approach is an advantage from an experimental perspective can only be answered by considering concrete physical systems and evaluating what the alternative approach amounts to for those system.

Pairing of fermions is ubiquitous in nature and it is responsible for a large variety of fascinating phenomena like superconductivity, superfluidity of 3He, the anomalous rotation of neutron stars, and the BEC-BCS crossover in strongly interacting Fermi gases. When confined to two dimensions, interacting many-body systems bear even more subtle effects, many of which lack understanding at a fundamental level. Most striking is the, yet unexplained, effect of high-temperature superconductivity in cuprates, which is intimately related to the two-dimensional geometry of the crystal structure. In particular, the question how many-body pairing is established at high temperature and whether it precedes superconductivity are crucial questions to be answered. We will report on recent experiments of pairing in a two-dimensional atomic Fermi gas in the regime of strong coupling. We perform angle-resolved photoemission spectroscopy to measure the spectral function of the gas and we observe a many-body pairing gap even above the predicted superfluid transition temperature.

Certain cold atoms, namely the alkaline earth-like atoms whose electronic degrees of freedom are decoupled from their nuclear spin, can be thought of as quantum particles with an SU(N)-symmetric spin. These have recently been cooled to quantum degeneracy in the laboratories around the world. A new world of SU(N) physics has thus become accessible to experiment, including that described by the SU(N) Hubbard model in various dimensions and by other related models. We show that the Mott insulator of such cold atoms is an SU(N) symmetric antiferromagnet of the type not commonly studied in the literature.  We further show that in 2 dimensions, this antiferromagnet is a chiral spin liquid, a long sought-after topological state of magnets, with fractional and non-Abelian excitations.  

Understanding the behaviors of strongly-interacting spin systems is one of the central objectives of modern manybody quantum physics. I will present experiments in which we have realized quantum magnetism with ultracold atoms in an optical lattice. We carry out a quantum simulation of an Ising spin chain and demonstrate a quantum phase-transition from a paramagnetic phase to an anti-ferromagnetic phase.The magnetic phases are detected in situ through our quantum gas microscope. This work opens a wide range of new possibilities for studying quantum magnetism. Exotic states of matter and frustrated spin physics in optical lattices are now within experimental reach.

The push to implement quantum information processing (QIP) with trapped ions has led to a number of technological advances that can be leveraged towards this goal, but also allow for novel experimental approaches outside the original scope. The most spectacular example for the latter is the quantum-logic ion clock, at present the most precise frequency standard, with potential for further improvement. This talk will cover some of the recent advances in QIP with trapped ions at NIST and give a few examples besides the quantum logic ion clock that illustrate the potential of trapped ions for quantum simulations of complex designer Hamiltonians, quantum limited measurements and high resolution spectroscopy.

On a sub-wavelength scale, atoms in a crystal, i. e. an ordered lattice, are normally assumed to be almost uniformly excited by an incident light. An interatomic interaction produces then a uniform local field (different from that of incident laser) at each atom as well. This is a major assumption in the Lorentz-Lorenz theory of interaction of light with dense matter. We showed [1] that at certain critical conditions on the atomic density and dipole strength, a previously unexpected phenomenon emerges: the interacting atoms break the uniformity of interaction, and in a violent switch to a strong non-uniformity, their excitation and local field form nanoscale strata with a spatial period much shorter than that of laser wavelength, thus changing the entire paradigm of light-matter interaction. The most interesting effects can be observed for relatively small 1D-arrays or 2D lattices if the laser is almost resonant to an atomic quantum transition. The effects include huge local field enhancement at size-related resonances at the frequencies near the atomic line, so that the strata are readily controlled by laser tuning. A striking feature is that for the shortest strata, the nearest atomic dipoles counter-oscillate, which is reminiscent of anti-ferromagnetism of magnetic dipoles in Ising model.

Diamond is not only the king gemstone, but also a promising material in modern technology (which holds a promise to replace silicon) owing to unprecedented thermal conductivity, high charge carrier mobility and chemical inertness. Less known is that defects in diamond can be used for quantum information processing. Owing to their remarkable stability, colour centers in diamond have already found an application in quantum cryptography.  Furthermore, it was shown that spin states associated with single nitrogen-vacancy defects can be detected optically. In this talk I will discuss recent progress regarding spin-based quantum information processing and atomic magnetometry using single spins in diamond.

Integrated optic devices – such as optical fibers, waveguides or linear optical circuits – in combination with pulsed quantum light and time-multiplexing configurations offer distinct advantages to realize photonic quantum systems for quantum information applications. The experimental setups get miniaturized, the spatial properties of generated quantum states are defined by the guiding geometries and networks are intrinsically stable. We present our toolbox for the realization of future quantum devices, including engineered genuine single-mode pulsed quantum light and a high dimensional quantum walk experiment.

Like all nanostructures, carbon nanotubes have interesting electromagnetic properties in the near field. The electromagnetic field near the cylindrical nanotube surface is affected by the electronic band structure, surface conductivity, and surface curvature of the nanotube. As a result, the interactions between the surface electromagnetic modes of the nanotube and, say, a surface excitonic state, or an atom (ion, molecule) doped into the nanotube have specific behaviors that have not been deeply explored thus far.