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Videos of Past Q-FARM Seminars

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Q-FARM Seminars are available on our YouTube channel, Q-FARM Stanford. Subscribe to receive notification of new recordings. Please note: not all seminars are recorded. 

May 19, 2022: Jonathan Home (ETH Zürich)

“Scalable approaches for ion trap quantum computing”

Quantum computing requires implementation of high fidelity control operations across an interconnected array of qubit systems. The requirements of quantum error correction put stringent limits on tolerable errors as well as introducing a larger overhead in the number of qubits. In this talk I will describe two approaches to the challenges of scaling trapped-ion quantum computers. The first is in the optical delivery, where we have recently demonstrated the first multi-qubit gates between ions using light delivered from trap-integrated waveguides. In further work, we have been investigating further possibilities arising from this technology, including the use of optical standing waves generated on-chip and protocols for entanglement generation. A second generation of photonic chips recently ordered from the foundry features modifications for blue light, tightly focused laser beams and better ion performance. I will then outline a new approach to implementing large scale quantum computing with trapped-ions based on micro fabricated Penning traps, also giving an insight into the physics of these systems and their advantages for scaling up.

May 18, 2022: Nathalie de Leon (Princeton University)

"Correlating materials analysis with qubit measurements to systematically eliminate sources of noise"

The nitrogen vacancy (NV) center in diamond exhibits spin-dependent fluorescence and long spin coherence times under ambient conditions, enabling applications in quantum information processing and sensing. NV centers near the surface can have strong interactions with external materials and spins, enabling new forms of nanoscale spectroscopy. However, NV spin coherence degrades within 100 nanometers of the surface, suggesting that diamond surfaces are plagued with ubiquitous defects. I will describe our recent efforts to correlate direct materials characterization with single spin measurements to devise methods to stabilize highly coherent NV centers within nanometers of the surface. We also deploy these shallow NV centers as a probe to study the dynamics of a disordered spin ensemble at the diamond surface and other sources of external noise.
 

May 6, 2022: Tobias Donner (ETH Zürich)

"Dissipative crystals of matter and light - from self-oscillating pumps to dissipation-stabilized phases"

The time evolution of a driven quantum system can be strongly affected by dissipation. Although this mainly implies that the system relaxes to a steady state, in some cases it can lead to the appearance of new phases and trigger emergent dynamics. I will report on experiments where we dispersively couple a quantum gas to an optical cavity. When the dissipation via cavity losses and the coherent timescales are comparable, we find a regime of persistent oscillations leading to a topological pumping of the atoms. Furthermore, I will report on the observation of a dissipation-stabilized phase in a system with tunable decay.

May 4, 2022: Immanuel Bloch (Max-Planck-Institute of Quantum Optics)

"From Kardar-Parisi-Zhang Superdiffusion in Heisenberg Quantum Magnets to Novel Quantum Optical Light Matter Interfaces with Subwavelength Atomic Arrays"

Quantum simulation with ultracold atoms has opened the avenue to probe non-equilibrium quantum many body dynamics in new parameters regimes and with completeley new detection techniques. In my talk, I will show how we utilize the high-resolution, single-spin sensitive detection afforded by a quantum gas microscope to track the out-of-equilibrium dynamics of Heisenberg quantum magnets in one and two dimension. Surprisingly, in 1D, the system exhibits a novel transport paradigm of anomalous superdiffusive transport compared to standard ballistic or diffusive transport scenarios. Additionally, by accessing the full counting statistics of transported spins, we find strong supporting evidence for the conjecture that transport in the XXZ chain at the Heisenberg point indeed falls in the so called Kardar-Parisi-Zhang universality class. I will explain the arguments for this conjecture and introduce the peculiar features of this anomalous transport regime.

April 6, 2022: Jack Harris (Yale University)

"Measuring the higher-order phonon-phonon coherences in a superfluid optomechanical device"

 I will describe measurements in which we detect the individual sideband photons produced by an optomechanical device consisting of a nanogram of superfluid helium confined in a cavity. We use the photon-counting data to probe the phonon-phonon correlations (up to fourth order) in a single acoustic mode of the superfluid. The data is consistent with the acoustic mode being in a thermal state with mean phonon number ~ 1. We also use sideband-photon counting to show that the acoustic mode can be driven to a coherent amplitude corresponding to tens of thousands of phonons without harming the state's purity. I will discuss applying these results to testing models of discrete spacetime, and to distributing entanglement over kilometer-scale optical fiber networks

March 23, 2022: Felipe H. da Jornada (Stanford University)

Understanding excited states in 2D and moiré materials for quantum applications

Low-dimensional materials, such as monolayer transition metal dichalcogenides (TMDCs), are marked by their spatial confinement, weak electronic screening, and large many-electron interactions. Such systems host a variety of multiparticle excitations – such as excitons, trions, biexcitons – often displaying large binding energies and long lifetimes even at room temperature. I will present new first-principles formalisms and calculations to understand the fingerprints of these excitations and their applicability for quantum science.

March 2, 2022: Rahul Trivedi (Max Planck Institute of Quantum Optics)

Non Markovian open quantum systems: Theoretical description and simulatability

Quantum systems arising in solid state physics, chemistry and biology invariably interact with their environment, and need to me modelled as open systems. While the theory of Markovian open quantum systems has been extensively developed, their non-Markovian generalization remains less well understood. In this talk, I will first review quantum stochastic calculus which provides a mathematically rigorous description of a unitary group generating Markovian sub-system dynamics. 

Feb. 2, 2022: Lorenzo Magrini (University of Vienna)

Quantum measurement and control of mechanical motion at room temperature

The Heisenberg uncertainty principle establishes the frontier to the quantum realm. The position of a particle, the spin of an atom, the energy of a photon can only be known with finite precision. Realizing measurements close to this limit requires high efficiency and good environmental isolation. 

November 17, 2021 Speaker: Abhay Pasupathy (Columbia University)

Quantum criticality in transition metal dichalcogenides

I will discuss low temperature transport measurements on twisted bilayers of WSe2, where we see evidence for an electron-correlation driven insulating phase at half filling of the lowest moiré subband. 

October 27, 2021 Speakers: Stanford PhD Candidates Ronen Kroeze & Eric Cooper

Two Talks

Talk #1: Here we present the realization of optical lattices with sound, using a Bose-Einstein condensate coupled to a confocal optical resonator.  Talk #2: Tunable interactions are an essential component of flexible platforms for quantum simulation and computation.  While most physical systems rely on local interactions dictated by the...

October 06, 2021 Speaker: Prof. Norman Yao (UC Berkeley)

Time Crystals in Open Systems

In this talk, I will describe recent advances, surrounding the idea of time translation symmetry breaking --- the resulting discrete time crystal exhibits collective subharmonic oscillations.

May 12, 2021 - Speaker: Brendan Marsh & Ognjen Marković (Stanford University)

Double Feature: Memory and optimization with multimode cavity QED; Transverse-Field Ising Dynamics by Rydberg Dressing in a cold atomic gas

In this first talk, I will describe how a driven-dissipative system is realized by coupling ultracold atoms to a multimode optical cavity and how it can perform various computational tasks. 

In this second talk, we will present a realization of long-range optically-controllable Ising interactions in a cold gas of cesium atoms by Rydberg dressing.

April 21, 2021 - Speaker: Valentina Parigi (Laboratoire Kastler Brossel – Sorbonne Université, Paris)

Quantum probes of two-dimensional materials

Spin qubits based on diamond NV centers can detect tiny magnetic fields; thin two-dimensional materials produce tiny magnetic fields.  Do they make a good match?  I will discuss two works that explored how NV magnetometry can uniquely probe the spins and currents in crystals that are ...

April 28, 2021 - Speaker: Ben Bartlett & Sunil Pai (Stanford University)

Double Feature: A photonic quantum computer design with only one controllable qubit; Towards MEMS-driven photonic computing

Talk #1: We describe a design for a photonic quantum computer which requires minimal quantum resources: a single coherently-controlled atom.

Talk #2: Programmable nanophotonic networks of Mach-Zehnder interferometers are energy-efficient circuits for matrix-vector multiplication that benefit a wide variety of applications such as artificial intelligence, quantum computing and cryptography.

April 21, 2021 - Speaker: Valentina Parigi (Laboratoire Kastler Brossel – Sorbonne Université, Paris)

Continuous variables quantum complex networks

Experimental procedures based on optical frequency combs and parametric processes produce quantum states of light involving large numbers of spectro-temporal modes that can be mapped and analyzed in terms of quantum complex networks.

April 14, 2021 - Speaker: Timothy P. McKenna (Stanford University) & Ryotatsu Yanagimoto (Stanford University)

Double Feature: Ultra-low-power second-order nonlinear optics on a chip; Quantum Dynamics of Ultrafast Nonlinear Photonics

Talk #1: Thin-film lithium niobate is a promising platform for integrated photonics because it can tightly confine light in small waveguides which allows for large interactions between light, microwaves, and mechanics.

Talk #2: Broadband optical pulses propagating in highly nonlinear nanophotonic waveguides can significantly leverage optical nonlinearity by tight temporal and spatial field confinements, promising a route towards all-optical quantum engineering and information with single-photon nonlinearities.

March 24, 2021 - Speaker: Avi Pe’er (Bar Ilan University)

Quantum sensing with unlimited optical bandwidth

Squeezed light is a major resource for quantum sensing, which has been already implemented in high-end interferometric sensing, such as gravitational wave detection. However, standard squeezed interferometry methods suffer from two severe limitations.

March 10, 2021 - Speaker: Natalia Berloff (University of Cambridge)

Unconventional computing with liquid light

The recent advances in the development of physical platforms for solving combinatorial optimisation problems reveal the future of high-performance computing for quantum and classical devices.

January 13, 2021 - Speaker: Debayan Mitra (Harvard University)

Direct laser cooling of polyatomic molecules

Laser cooling and evaporative cooling are the workhorse techniques that have revolutionized the control of atomic systems.

December 2, 2020 - Speaker: Kartik Srinivasan (University of Maryland/NIST Joint Quantum Institute)

Towards quantum and classical light sources and transducers at any wavelength using nonlinear nanophotonics

Nanophotonics provides the unprecedented opportunity to engineer nonlinear optical interactions through the nanometer-scale control of geometry provided by modern fabrication technology.