## Research overview:

How much knowledge can we obtain about a physical system and to what degree can we control it? At the microscopic level, the answer to this question is dictated by the laws of quantum mechanics. For example, few-particle quantum-optics systems, such as trapped ions or atoms in cavities, are now controlled and probed at the fundamental level of individual quanta.

In contrast, large collections of interacting quantum particles, such as electrons in a solid, pose entirely new challenges due to the enormous number of microscopic parameters and the resulting difficulties in describing and detecting their quantum state. At the same time, they also offer new opportunities for applications such as quantum computing, quantum simulation and precision measurements.

Our group investigates quantum many-body systems using methods from quantum-optics, atomic, molecular and optical (AMO) physics, and nanophotonics. Particularly, we develop novel techniques for probing and manipulating many-particle quantum systems at the level of

We believe in a highly collaborative approach to research that crosses boundaries between AMO physics, quantum information, and quantum many-body physics while integrating experiments and theoretical investigations. At Caltech, the Institute for Quantum Information and Matter provides a unique, stimulating environment and we work with colleagues from several research institutions, such as Harvard, the Max-Planck Institute for Quantum Optics, TU Munich and Scuola Normale Superiore Pisa.

In contrast, large collections of interacting quantum particles, such as electrons in a solid, pose entirely new challenges due to the enormous number of microscopic parameters and the resulting difficulties in describing and detecting their quantum state. At the same time, they also offer new opportunities for applications such as quantum computing, quantum simulation and precision measurements.

Our group investigates quantum many-body systems using methods from quantum-optics, atomic, molecular and optical (AMO) physics, and nanophotonics. Particularly, we develop novel techniques for probing and manipulating many-particle quantum systems at the level of

*individual*quantum particles, such as, atoms, photons, or spins. For example, we work on the assembly of quantum many-body systems in an atom-by-atom fashion or explore novel avenues for quantum microscopy of ultracold atoms in optical lattices.We believe in a highly collaborative approach to research that crosses boundaries between AMO physics, quantum information, and quantum many-body physics while integrating experiments and theoretical investigations. At Caltech, the Institute for Quantum Information and Matter provides a unique, stimulating environment and we work with colleagues from several research institutions, such as Harvard, the Max-Planck Institute for Quantum Optics, TU Munich and Scuola Normale Superiore Pisa.

## Examples of current research topics:

**Single-particle control of strontium atoms:**

We are currently setting up a novel experiment for single-atom control of neutral Strontium with the long-term purpose of scalable atom-by-atom assembly of strongly-correlated 2d systems. Strontium's two valence-electron structure offers a number of advantages including narrow optical transitions, largely decoupled storage states, and interesting Rydberg properties.

**Detection of dynamical correlation functions:**

In collaboration with Michael Knap's group at TU Munich, we are exploring new techniques for measuring dynamical correlation functions, including out-of-time ordered functions.

**Effects of dynamically changing Berry phases:**

In collaboration with Gil Refael, we are exploring effects of dynamically changing Berry phases in optical lattices.

**Atom-array on-demand generation:**

In collaboration with Misha Lukin's group at Harvard, we are exploring novel ways for generating arrays of atoms in a particle-by-particle fashion. This opens up new avenues for quantum simulation and information architectures, for example, using Rydberg or photon-induced interactions. We are currently able to assemble 1d arrays of about 50 atoms in 200ms.

## Examples of further research topics:

Entanglement detection: In collaboration with the Rosario Fazio's group, we theoretically proposed a method for spin-entanglement detection in optical lattices that was subsequently experimentally realized in a collaboration with the Bloch group. |

Optical lattice version of strained graphene: In collaboration with David Pekker's group, we proposed a method to generate relativistic Landau levels by straining an optical lattice |

**Coupling of atoms to nanophotonic structures:**

In collaboration with Misha Lukin's group, we are coupling individual Rubidium atoms to one-dimensional photonic crystal structures enabling interactions between the atoms and single photons. Our main goal is to extend the scheme to multiple atoms for entanglement generation and photon-induced atom-atom interactions.

Wilson loops as probes for Bloch band topology: In collaboration with the Bloch group, we are working on novel ways to probe the geometry of Bloch bands using Wilson loops and lines. |

Development of a quantum microscope for optical lattices: Development of a novel method for imaging and manipulating individual atoms in optical lattices. |

Detection of a Higgs mode close to a 2d quantum phase transition: We observed an amplitude ‘Higgs’ modes close to the 2d superfluid-Mott insulator transition by measuring the dynamical response to lattice modulation with single-atom-sensitivity. The observability of ‘Higgs’ modes close to 2d quantum phase transitions has been debated and our measurements helped to resolve the discussion. |

Two-site and non-local correlation functions: Using the quantum microscope, we detected correlation functions at the single particle level including a proof-of-principle that nonlocal observables are experimentally accessible. Such nonlocal quantities, taking into account detailed information of extended regions, are necessary for describing order in quantum phases that are beyond the standard Landau description (e.g., topological phases). |

Out-of-equilibrium dynamics of correlations: Experimental observation of light-cone spreading of two-site correlations after a quantum quench of 1d Mott insulators. |

**Quantum dynamics of individual spins and magnon bound states:**

We prepared individual spin impurities using single atom addressing and watched their dynamics.

**Theory for nonlocal correlations:**

We worked out a theoretical extension of nonlocal order to 2d systems showing that area correlations correspond to spatial Wilson loops in a dual description. Further, we theoretically investigated the out-of-equilibrium dynamics of non-local correlations.