JQI Seminar

Abstract: Quantum computers hold the promise of solving computational problems which are intractable using conventional methods. For fault-tolerant operation quantum computers must correct errors occurring due to unavoidable decoherence and limited control accuracy. Here, we demonstrate quantum error correction using the surface code, which is known for its exceptionally high tolerance to errors. Using 17 physical qubits in a superconducting circuit we encode quantum information in a distance-three logical qubit building up on recent distance-two error detection experiments [1].

Prethermalization has been extensively studied in systems close tointegrability. We discuss a more general, yet conceptually simpler, setup forthis phenomenon. We consider a--possibly nonintegrable--reference dynamics,weakly perturbed so that the perturbation breaks at least one conservationlaw. We argue then that the evolution of the system proceeds via intermediate(generalized) equilibrium states of the reference dynamics. The motion on themanifold of equilibrium states is governed by an autonomous equation, flowing

Engineering coherent systems is a central goal of quantum science and quantum information processing. Point defects in diamond known as color centers are a promising physical platform. As atom-like systems, they can exhibit excellent spin coherence and can be manipulated with light. As solid-state defects, they can be produced at high densities and incorporated into scalable devices. Diamond is a uniquely excellent host: it has a large band gap, can be synthesized with sub-ppb impurity concentrations, and can be isotopically purified to eliminate magnetic noise from nuclear spins.

This talk will review applications of quantum simulators that make use of machine learning techniques. Snapshots of many-body states obtained from quantum gas microscopes can be used to perform hypothesis testing using convolutional neural networks. The application of this technique to the Fermi Hubbard model has demonstrated that geometrical string model provides a better description of the experimental data than the pi-flux RVB model. I will also discuss the idea of combing quantum simulators with machine learning to perform inference of NMR spectra for small biological molecules.

Time-reversal symmetry is a defining property for wave phenomena in linear stationary media. However, broken time-reversal symmetry is required for producing essential nonreciprocal devices like isolators, circulators, and gyrators. Magneto-optic methods can enable nonreciprocal behavior for electromagnetic waves, but this approach does not readily translate to the microscale or for atomic-PNT technologies, compelling us to search for nonmagnetic solutions.

Pioneered by topological insulators and semimetals, topological states of matter have shaped a significant part of contemporary condensed matter physics, and have largely branched out into adjacent fields such as photonics, mechanics, and other metamaterial setups. Recently, the frontier has shifted to topological systems which embody enrichments such as non-Hermiticity and non-linearity.

Experiments frequently come with surprises. In this talk, I will describe the story behind the discovery of Bose fireworks, a sudden emission of matterwave jets from a driven Bose-Einstein condensate. The jet emission originates from collective scattering of atoms, seeded by quantum fluctuations and amplified by bosonic stimulation. The process results in an intricate jet emission pattern resembling those observed in high-energy collisions of heavy ions as well as Unruh radiation near the event horizon.

A new type of superlattice, known as the moiré superlattice, forms when two monolayers of van der Waals materials are vertically stacked. The period of the moire superlattice is readily controlled by the lattice constant mismatch and the twist angle. The energy modulation within a supercell varies as much as a few hundred meV, effectively trapping carriers and excitons. These superlattices exhibit a host of rich properties that may find applications in quantum information science such as an array of single quantum emitters and quantum simulations. 

Topological superconductors represent a fundamentally new phase of matter. Similar to topological insulators, the non-trivial topological characteristics of a topological superconductor dictate the presence of a topological edge states composed of Bogoliubov quasiparticles which live inside and span the superconducting gap.

Quantum dots are often described as artificial atoms because they have discrete energy levels analogous to those of natural atoms. Solid state quantum dots (e.g. InAs in GaAs) can be extended from artificial atoms to artificial molecules by controlling the relative spatial proximity and orientation of a pair of quantum dots. These pairs of dots are called quantum dot molecules (QDMs) because coherent tunnel coupling between the individual quantum dots leads to the formation of molecular states analogous to those in diatomic molecules.