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QFarm

QFarm Quantum Seminar Series

Q-FARM presents "Lattice atom interferometry in an optical cavity"

Topic: 
Lattice atom interferometry in an optical cavity
Abstract / Description: 

Atom interferometers are powerful tools for both measurements in fundamental physics and inertial sensing applications. Their performance, however, has been limited by the available interrogation time of atoms freely falling in a gravitational field. I will describe our realization of an intra-cavity trapped atom interferometer with 20 seconds of coherence, which extends the interrogation time of spatially-separated quantum superpositions of massive objects by nearly an order of magnitude. I will discuss how this trapped geometry differs from traditional free-fall atom interferometers by allowing potentials to be measured by holding, rather than dropping, atoms.

Date and Time: 
Wednesday, November 25, 2020 - 12:00pm
Venue: 
Zoom ID: 987 676 025; +Password

Q-FARM presents "Wildcard error: Quantifying unmodeled errors in quantum processors"

Topic: 
Wildcard error: Quantifying unmodeled errors in quantum processors
Abstract / Description: 

Error models for quantum computing processors describe their deviation from ideal behavior and predict the consequences in applications. But experimental behavior is rarely consistent with error models, even in characterization experiments like randomized benchmarking (RB) or gate set tomography (GST). I show how to resolve these inconsistencies, and quantify the rate of unmodeled errors, by augmenting error models with a parameterized wildcard error model. Wildcard error relaxes the model's predictions, and the amount of wildcard error required (to reconcile the model with observed data) quantifies the rate of unmodeled errors. I'll demonstrate the use of wildcard error to augment RB and GST, and to quantify leakage.

Date and Time: 
Wednesday, November 18, 2020 - 12:00pm
Venue: 
Zoom ID: 987 676 025; +Password

QFARM Quantum Seminar Series presents "Millimeter-wave photons for quantum science"

Topic: 
Millimeter-wave photons for quantum science
Abstract / Description: 

Millimeter-wave frequencies (30-300GHz) provide a promising platform for quantum information technology at less explored but potentially beneficial length and energy scales. In this talk, I will discuss the advantages of the mm-wave band and describe our hybrid quantum system for entangling and inter-converting single mm-wave and optical photons using Rydberg atoms as mediators. I will go over our experimental progress and potential applications of our system for frequency transduction and quantum nonlinear photonics. To conclude, I will describe some applications of mm-wave photons we have explored for 2D nonlinear devices, photonic crystals, and twisted mm-wave Fabry-Perot cavities.

Date and Time: 
Wednesday, October 28, 2020 - 12:00pm
Venue: 
Zoom meeting ID: 987 676 025; password required

Q-FARM presents "Fast Optimization of Photonic Circuits for Automated Device Design"

Topic: 
Fast Optimization of Photonic Circuits for Automated Device Design
Abstract / Description: 

Photonic circuits are a promising platform for quantum computation and quantum communication: they don't require low temperatures or vacuum to operate and they can be built on a small chip. It would be wonderful to be able to design photonic circuits for any desired purpose, however in general this is a difficult task which we would much rather automate. In this talk I will present a new method to optimize photonic circuits (through differentiable simulation), which is about 100x faster than the previous state of the art. This allows us to automate the design of photonic devices, by starting with a random circuit and optimizing it until it achieves the desired behaviour. The added speed of our method allows us to design larger circuits and to achieve a much higher accuracy than it was previously possible. The talk is designed to be accessible to non-experts and will cover the basics of quantum optics, optical gates, photonic circuits and differentiable simulation.

Date and Time: 
Wednesday, September 30, 2020 - 12:00pm
Venue: 
Zoom ID: 987 676 025; +password

Q-FARM presents "Scaling-up single-photon quantum hardware towards quantum-information processing with a quantum advantage"

Topic: 
Scaling-up single-photon quantum hardware towards quantum-information processing with a quantum advantage
Abstract / Description: 

Semiconductor quantum dots embedded in photonic nanostructures offer a highly efficient and coherent deterministic photon-emitter interface [1]. It constitutes an on-demand single-photon source for quantum-information applications, enables single-photon nonlinear, optics and the constructing of deterministic quantum gates for photons [2]. We review recent experimental progress, and demonstrate that the current technology can be scaled up to reach quantum advantage [3] with the demonstration of near-transform-limited emitters in high-cooperativity planar nanophotonic waveguides [4]. The coherent control of a single spin in the quantum dot [5, 6] offers additional opportunities of generating advanced multi-photon entangled states [7]. We finally discuss how this emergent hardware may be applied in a resource-efficient manner, e.g., for constructing a one-way quantum repeater [8].

References

[1] Lodahl et al., Rev. Mod. Phys. 87, 347 (2015).
[2] Lodahl, Quantum Science and Technology 3, 013001 (2018).
[3] Uppu et al., Arxiv: 2003.08919.
[4] Pedersen et al., ACS Photonics (2020).
[5] Javadi et al., Nature Nanotechnology 13, 398 (2018).
[6] Appel et al., Arxiv: 2006.15422.
[7] Tiurev et al., Arxiv: 2007.09295.
[8] Borregaard et al., Phys. Rev. X 10, 021071 (2020).

Date and Time: 
Wednesday, September 23, 2020 - 12:00pm
Venue: 
Zoom meeting ID: 987 676 025; password required.

Q-FARM presents "Demonstrating different advantages in quantum processing"

Topic: 
Demonstrating different advantages in quantum processing
Abstract / Description: 

Quantum computing famously promises an exponential speedup in runtime for universal computation applications such as code breaking and simulation. However, it is possible to identify a number of processing tasks—perhaps of a different nature—for which other quantum advantages exist. I'll give an overview of three such tasks: a memory advantage in stochastic simulation; a communication advantage in distributed processing; and a resource advantage in transforming probability distributions. I'll describe the photonic experimental realisation of one or two of these.

Date and Time: 
Wednesday, September 16, 2020 - 3:00pm
Venue: 
Zoom Meeting ID: 987 676 025; +Password

Q-FARM Quantum Seminar Series presents "Restrictions on logical gates in quantum error correction"

Topic: 
Restrictions on logical gates in quantum error correction
Abstract / Description: 

The disjointness for stabilizer codes in quantum error correction is an algebraic quantity tied to the structure of the stabilizer generators of a code. It can be used to characterize the properties of different classes of logical gates, placing bounds on the level of the Clifford hierarchy attainable by constant depth circuits. This talk will introduce the notion of disjointness, highlight its usefulness with several examples, and posit open questions for which the disjointness may be useful in addressing.

Date and Time: 
Wednesday, September 2, 2020 - 12:00pm
Venue: 
Zoom ID: 987 676 025; +password

Q-FARM presents "Free-Electron Quantum Optics"

Topic: 
Free-Electron Quantum Optics
Abstract / Description: 

Research of cavity quantum electrodynamics (CQED) has enabled new capabilities in quantum optics, quantum computation, and various quantum technologies. So far, all the work in this field has included light interacting with bound-electron systems such as atoms, quantum dots, and quantum circuits. In contrast, free-electron systems enable fundamentally different physical phenomena, as their energy distribution is continuous and not discrete, and allow for tunable transitions and selection rules.

We have developed a platform for studying free-electron CQED at the nanoscale and demonstrated it by observing coherent electron interaction with a photonic cavity for the first time. Our platform includes femtosecond lasers in an ultrafast transmission electron microscope, which created what is, in many respects, the most powerful nearfield optical microscope in the world today. We resolve photonic bandstructures as a function of energy, momentum, and polarization, simultaneously with capturing the spatial distribution of the photonic modes at deep-subwavelength resolution.

These capabilities open new paths toward using free electrons as carriers of quantum information. As examples, we show how to create free-electron qubits and implement quantum gates with femtosecond lasers. We further show how to measure quantum decoherence in space and time using the free-electron quantum interactions. Such interactions also enable new avenues for tunable X-ray sources, as we demonstrate with theory and experiments.

Date and Time: 
Wednesday, August 19, 2020 - 10:00am
Venue: 
Meeting ID: 987 676 025 (+ password)

Q-FARM presents "Large-Scale Quantum Photonic Processors"

Topic: 
Large-Scale Quantum Photonic Processors
Abstract / Description: 

Photons play a central role in many areas of quantum information science, either as qubit themselves or to mediate interactions between long-lived matter based qubits. Techniques for (1) high-fidelity generation, (2) precise manipulation and (3) ultra-efficient detection of quantum states of light are therefore a prerequisite for virtually all quantum technologies. A quantum photonic processor is the union of these three core technologies into a single system, and, bolstered by advances in integrated photonics, promises to be a versatile platform for quantum information science and beyond. In this talk I present recent progress towards large-scale quantum photonic processors and demonstrate how such systems enable new applications at the nexus of quantum mechanics and machine learning.

Date and Time: 
Wednesday, August 5, 2020 - 12:00pm
Venue: 
ZOOM ID: 987 676 025

Q-FARM presents "Quantum Metrology in the Era of Quantum Information"

Topic: 
Quantum Metrology in the Era of Quantum Information
Abstract / Description: 

I will review the most recent advances in the theoretical methods of quantum metrology, focusing on the quantum information related concepts such as quantum error-correction and matrix product states formalism. The aim of the talk is to show how the two fields, quantum metrology and quantum information, are closely connected and how they can benefit from each other. The talk will be based on three papers:

[1] R. Demkowicz-Dobrzanski, J. Czajkowski, P. Sekatski, Adaptive quantum metrology under general Markovian noise, Phys. Rev. X 7, 041009 (2017)

[2] K. Chabuda, J. Dziarmaga, T. J. Osborne, R.Demkowicz-Dobrzanski, Tensor-Network Approach for Quantum Metrology in Many-Body Quantum Systems, Nat. Commun. 11, 250 (2020)

[3] A. Kubica, R. Demkowicz-Dobrzanski, Using Quantum Metrological Bounds in Quantum Error Correction: A Simple Proof of the Approximate Eastin-Knill Theorem, arXiv:2004.11893 (2020)

 

Password via qfarm-contact@stanford.edu

Date and Time: 
Wednesday, July 22, 2020 - 10:00am
Venue: 
Meeting ID: 987 676 025; + password)

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