Quantum Huddle Seminar Series

Abstract: We describe how various quantum optics techniques can be exploited to engineer both single-particle and effective interaction terms in solid-state systems. We start by electronic quantum Hall systems and show how optical selection rules are modified and how an effective interaction can be generated using an optical drive. We also investigate whether anyonic excitation can be optically generated and manipulated. Moreover, we discuss how patterned light can lead to superlattice structures for electrons, including flatland, kagome lattice, etc. In the end, we discuss how optical manipulation, such as optical pumping and bath engineering, could provide a new way to enhance superconductivity.

Abstract: Levitated optomechanics exploits the forces of light to suspend nanoscopic objects in vacuum. The light field serves both as a handle to mechanically manipulate, but also to interrogate various mechanical degrees of freedom of a levitated particle. In our talk, we introduce the audience to the field of levitated optomechanics, and discuss recent experimental progress towards full optomechanical control of the rotational and translational degrees of freedom of a levitated nanoparticle. In particular, we focus on feedback cooling a levitated particle’s motion to the few-phonon regime, where first signatures of its motional ground state emerge.

Abstract: A nanoscale gap between two metallic nanoparticles is an ideal platform to exploit the interplay between electron currents and photonic excitations. The capability of a metallic gap to enhance the amplitude of the induced plasmonic field produces a variety of non-linear effects which can be exploited in different applications in optoelectronics, such as optical rectification, light emission driven by DC currents, or high-harmonic generation, among others. Furthermore, in ultranarrow gaps, tunneling of electrons at optical frequencies has been found to screen the plasmonic bonding gap resonance, and activate a new distribution of optical modes characterized by optical charge transfer. Here we address the complex dynamics of photoelectrons driven by single-cycle optical pulses in nanoscale gaps. By solving Schrödinger equation within the framework of Time-Dependent Density Functional Theory (TDDFT), the currents of the electrons photoemitted across the gap can be monitored, identifying ultrafast electron bursts where electron quiver occurs when the amplitude of the induced field at the plasmonic gap is reversed within the optical cycle. The properties of the amplitude and carrier-envelope phase (CEP) of the incident pulse, together with the gap length determine the complex electron dynamics. Experimental measurements of the current autocorrelations for pairs of such pulses with controlled relative delay between them, confirms the ultrafast dynamics of the photoelectrons in the gap and its complexity.

Abstract: Quantum computation promises an exponential speedup of certain classes of classical calculations through the preparation and manipulation of entangled quantum states. So far most molecular simulations on quantum computers, however, have been limited to small numbers of particles. In this talk I will discuss our research group's recent preparation of a highly entangled state on a 53-qubit IBM quantum computer, representing 53 particles, which reveals the formation of an exciton condensate of photon particles and holes. More generally, I will discuss recent research efforts in our group directed towards exploiting the potential advantage of quantum computing for chemistry.

Abstract: Here, I will present several examples demonstrating how the new generation of monochromators, aberration-correctors and cameras in STEM can rival the capabilities of synchrotrons and allow to probe materials behavior at the nanometer and atomic scales in complete new ways. Specifically, I will show how by utilizing the phase of the electron probe one can reveal the anti-ferromagnetic order of complex-oxide materials [1], and explore the ferromagnetic strength at the interfaces of thin-film complex-oxide heterostructures [2] at the atomic level. I will also explain how STEM can be used to detect site-specific isotopic labels in amino acids at the nanometer scale [3], and show our current efforts in obtaining a vibrational spectroscopy atlas of all proteinogenic amino acids via EELS. Lastly, I will discuss potentially relevant new challenges that electron microscopy will need to resolve in the future. Would it be possible to map orbitals and spins with atomic resolution and with single atom sensitivity? Could we detect a superconducting transition? Could we detect minute concentrations of isotopic elements and perform radiocarbon dating at the nanoscale? These questions will be addressed and further elaborated during the presentation [4]. References: [1] J. C. Idrobo, et al., Adv. Struc. Chem. Img. 2 (2016), p. 5. [2] J. C. Idrobo, et al., unpublished (2020). [3] J. A. Hachtel, et al., Science 363 (2019), p. 525. [4] This research was supported by the Center for Nanophase Materials Sciences, which is a Department of Energy Office of Science User Facility, and instrumentation within ORNL's Materials Characterization Core provided by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy.

Abstract: Chemistry offers an atomically precise way to synthesize qubits. By harnessing chemical precision we can place atoms exactly where we want them. Research on constructing chemical qubits and understanding their coherence properties will be presented. Recent results on creating optically addressable molecular qubits or molecular color centers will be highlighted.

Abstract: I will describe our experiments to drive spin and orbital resonance of single diamond nitrogen-vacancy (NV) centers using the gigahertz-frequency strain oscillations produced within a diamond acoustic resonator. Strain-based coupling between a resonator and a defect center takes advantage of intrinsic and reproducible coupling mechanisms while maintaining compatibility with conventional magnetic and optical techniques, thus providing new functionality for quantum-enhanced sensing and quantum information processing. Using a spin-strain interaction at room temperature, we demonstrate coherent spin control over both double quantum (Δm=±2) and single quantum (Δm=±1) transitions. At cryogenic temperatures, we use orbital-strain interactions driven by a diamond acoustic resonator to study multi-phonon orbital resonance of a single NV center. Additionally, I’ll describe our efforts to enhance electron-phonon coupling by engineering mechanical resonators with small modal volumes based a semi-confocal acoustic cavity.

Abstract: Spin-photon interfaces augmented with quantum memories can be used as quantum repeater nodes, which are critical components of quantum communication networks. We will present our theoretical work toward the realization of quantum repeaters, focusing on the triggered generation of entangled photonic graph states from a spin-photon interface and the control of nuclear spin registers coupled to a color center spin.

Abstract: The sustained storage, transmission, or processing of quantum information will likely be a non-equilibrium process that requires monitoring the system and applying some form of feedback to produce fault-tolerance. Achieving this paradigm in near-term quantum devices faces challenging resource constraints. In this talk, I will discuss a class of models based on random quantum circuit dynamics interspersed with projective measurements that display a similar phenomenology to models for fault-tolerance, including the existence of a threshold, but with many helpful simplifications for theoretical analysis. Quantum Shannon theory and quantum error correction play a central role in our analysis. A major corollary of our results is to establish the existence of a novel set of dynamically generated quantum error correcting codes whose study may provide broader lessons for resource-limited fault-tolerance. I will then discuss a scheme to probe the phase transition in these models on near-term quantum computing devices.

Abstract: Tightly packed ordered arrays of atoms (or, more generally, quantum emitters) exhibit remarkable collective optical properties. In this talk, we will discuss the few- and many-body out-of-equilibrium physics of 1D arrays. For small enough lattice constants, such chains feature dark states that allow for dissipationless transport of photons, behaving as waveguides. These atomic waveguides can be used to mediate interactions between impurity qubits coupled to the array. Due to the two-level nature of the atoms, atomic waveguides are a perfect playground to realize strong photon-photon interactions. At the many-body level, collective decay leads to superradiance even for finite inter-atomic separation. Signatures of photon-photon correlations and directional emission can be measured in state of the art experiments.