
Alkaline earth atoms in tweezer arrays for quantum simulation, quantum optimization and quantumenhanced metrology:
Recently, cold atoms in optical tweezer arrays have emerged as a versatile platform for quantum science experiments. Specifically, ''atombyatom assembly'' [1] now provides a fast and simple method for generating defectfree atomic arrays, which are used as qubit registers. Entanglement is generated in a highly controlled fashion via excitation to Rydberg states, which interact strongly at typical interatomic distances. Applications of such 'Rydberg Arrays' range from quantum simulation and quantum computing to quantum optimization tasks. While already reaching highly competitive results, these systems are still in their infancy. 
Our group uses alkaline earth atoms to improve upon existing limitations and to open new avenues in quantum metrology. Some of our recent highlights include:
1) A record in imagingfidelity for neutral atoms and demonstration of narrowline cooling in tweezers [2,3].
2) Highfidelity Rydberg excitation from a clock state, including a record in entanglementfidelity for two neutral atoms [4].
3) Demonstration of an optical clock with singleatom detection in tweezer arrays [5].
Current efforts target highfidelity operations and their verification in largescale arrays and subsequent application to quantum simulation, quantumenhanced metrology as well as quantum optimization.
[1] Endres et al., Science 354, 1024 (2016)
[2] Covey et. al, Phys. Rev. Lett. 122, 173201 (2019)
[3] Cooper et al., Phys. Rev. X 8, 041055 (2018)
[4] Madjarov*, Covey*, et al., Nature Physics (2020)
[5] Madjarov et al., Phys. Rev. X 9, 041052 (2019)
1) A record in imagingfidelity for neutral atoms and demonstration of narrowline cooling in tweezers [2,3].
2) Highfidelity Rydberg excitation from a clock state, including a record in entanglementfidelity for two neutral atoms [4].
3) Demonstration of an optical clock with singleatom detection in tweezer arrays [5].
Current efforts target highfidelity operations and their verification in largescale arrays and subsequent application to quantum simulation, quantumenhanced metrology as well as quantum optimization.
[1] Endres et al., Science 354, 1024 (2016)
[2] Covey et. al, Phys. Rev. Lett. 122, 173201 (2019)
[3] Cooper et al., Phys. Rev. X 8, 041055 (2018)
[4] Madjarov*, Covey*, et al., Nature Physics (2020)
[5] Madjarov et al., Phys. Rev. X 9, 041052 (2019)
Theory projects:
Quantum behavior and control of strongly interacting arrays:
We are exploring various new ideas for employing Rydberg arrays, and other longrange interacting spin systems, in quantum simulation, quantum information, entangled state engineering, and quantum metrology. Projects range from more abstract questions to realistic modeling of experimental scenarios, including open system dynamics.
We are exploring various new ideas for employing Rydberg arrays, and other longrange interacting spin systems, in quantum simulation, quantum information, entangled state engineering, and quantum metrology. Projects range from more abstract questions to realistic modeling of experimental scenarios, including open system dynamics.
Verification and readout methods:
We are exploring new methods for readout of complex observables and for verification of largescale quantum devices.
We are exploring new methods for readout of complex observables and for verification of largescale quantum devices.
Examples of previous Research topics:
Alkalineearth atoms for quantum communication
In collaboration with Oskar Painter's group at Caltech, we worked out a new idea for quantum communication based on individually controlled alkalineearth atoms coupled to cavity systems in the telecom range.
In collaboration with Oskar Painter's group at Caltech, we worked out a new idea for quantum communication based on individually controlled alkalineearth atoms coupled to cavity systems in the telecom range.
Use of machinelearning techniques in quantum simulation experiments and manybody theory
We are investigating the use of machinelearning techniques applied to questions in quantum many body theory and experiments, specifically concerning quantum state reconstruction and numerical manybody methods in 2d.
We are investigating the use of machinelearning techniques applied to questions in quantum many body theory and experiments, specifically concerning quantum state reconstruction and numerical manybody methods in 2d.
Effects of dynamically changing Berry phases:
In a theory collaboration with Gil Refael, we are exploring effects of dynamically changing Berry phases in optical lattices.
In a theory collaboration with Gil Refael, we are exploring effects of dynamically changing Berry phases in optical lattices.
Rydberg array quantum simulation with alkali atoms:
In collaboration with Misha Lukin's group at Harvard, we have been developing new techniques for quantum simulations based on Rydberg atom arrays. These experiments are based on atombyatom assembly of defectfree atomic arrays with optical tweezer.
In collaboration with Misha Lukin's group at Harvard, we have been developing new techniques for quantum simulations based on Rydberg atom arrays. These experiments are based on atombyatom assembly of defectfree atomic arrays with optical tweezer.
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 outoftime ordered functions.
In collaboration with Michael Knap's group at TU Munich, we are exploring new techniques for measuring dynamical correlation functions, including outoftime ordered functions.
Entanglement detection:
In collaboration with the Rosario Fazio's group, we theoretically proposed a method for spinentanglement 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 onedimensional 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 photoninduced atomatom interactions.
In collaboration with Misha Lukin's group, we are coupling individual Rubidium atoms to onedimensional 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 photoninduced atomatom 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 superfluidMott insulator transition by measuring the dynamical response to lattice modulation with singleatomsensitivity. The observability of ‘Higgs’ modes close to 2d quantum phase transitions has been debated and our measurements helped to resolve the discussion. 
Twosite and nonlocal correlation functions:
Using the quantum microscope, we detected correlation functions at the single particle level including a proofofprinciple 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). 
Outofequilibrium dynamics of correlations:
Experimental observation of lightcone spreading of twosite 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.
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 outofequilibrium dynamics of 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 outofequilibrium dynamics of nonlocal correlations.