Canada

Optically active defects in solids---colour centres---are one of the most promising platforms for implementing quantum technologies. Their spin degrees of freedom serve as quantum memories that in some cases can operate at room temperature. Their control can be achieved with microwave spin control and resonant optical excitation but is hindered by the broadening of optical transitions from thermal phonons and spectral diffusion. Furthermore, spin-qubit optical transitions are often outside the telecommunications wavelength band required for long-distance fiber optic transmission. Harnessing the coupling between mechanical degrees of freedom and spins has emerged as an alternative route for controlling spin-qubits. However, connecting spin-mechanical interfaces to optical links to realize a spin-photon interface has remained a challenge. Here we demonstrate such an interface using a diamond optomechanical cavity that does not depend on optical transitions and can be applied to a wide range of spin qubits.
Our device consists of a diamond microdisk resonator studied in [Optica 3, 963-970 (2016)]. The microdisk is fabricated from optical grade diamond that contains ensembles of NV centres. We use an optical mode at 1564 nm with the quality factor Qo = 150k. The mechanical mode which we use to couple to the NV spin state is a radial breathing mode with a frequency of around 2.1 GHz with the quality factor Qm = 4k. The device operates in the sideband resolved regime enabling optomechanical self-induced oscillations for sufficiently high optical input power of a blue detuned laser. These oscillations can produce the stress of a few MPa, large enough to drive the electronic spins of NV centers. We use a standard diamond NV confocal microscope to initialize and readout the NV state. The MW pulses transfer the population between |-1⟩&lt;-&gt;|0⟩ and |+1⟩&lt;-&gt;|0⟩ state. We wait for 0.7 us with the mechanical drive that drives the |-1⟩&lt;-&gt;|+1⟩ transition. 
In our measurements, we observe a coinciding dip in the |+1⟩ population and a peak |-1⟩ population, that verifies that the spins are being optomechanically driven. On calibrating this signal with the MW Rabi contrast and the background signal, we estimate a driving rate of 2pix170kHz and ~45% transfer of spin population between |±1⟩ states. Feasible improvements in device geometry will increase the optomechanically-induced driving rate by a few orders of magnitude allowing for coherent control of NV spins using an optomechanical resonator.

CAP Virtual Congress 2021

Optomechanical interface between telecom photons and spin quantum memory

solid-state qubit

quantum transducer

quantum communication

The Institute of Physics and IOP Publishing, in partnership with the Chinese Physical Society (CPS) and the University of Science and Technology of China (USTC) are proud to have brought together the international quantum science community online for this inaugural conference.


Early career and leading researchers from universities, industry and government worldwide came together to share, learn and collaborate on the latest research and emerging areas of high interest across quantum science and technology. The broad themes covered by Quantum 2020 included:

Quantum communication;
Quantum computing and quantum simulation;
Quantum sensing, metrology and imaging;
Quantum information theory, software and algorithms;
Quantum foundations;
Quantum technology in industry.
The four-day event featured talks from world-renowned scientists, interactive poster sessions and two exciting panel discussions on the themes of Quantum Technology in Industry and Quantum Technology Programmes Around the World.


You will need to [register](https://www.iopconferences.org/iop/frontend/reg/tRegisterEmailNew.csp?pageID=978403&eventID=1552&tempPersonID=536224) to obtain a ticket. . If you have already registered you should have been sent an email from Underline (to the email address that you registered with) with the subject line ‘Welcome to Quantum 2020’. This email includes your ticket for the event. 

If you have a ticket and are experiencing problems in accessing the event, please contact us. 

Quantum 2020

The Institute of Physics and IOP Publishing, in partnership with the Chinese Physical Society (CPS) and the University of Science and Technology of China (USTC) are proud to have brought together the international quantum science community online for this inaugural conference.

Early career and leading researchers from universities, industry and government worldwide came together to share, learn and collaborate on the latest research and emerging areas of high interest across quantum science and technology. 

Optically active defects in solids---colour centres---are one of the most promising platforms for implementing quantum technologies. Their spin degrees of freedom serve as quantum memories that in some cases can operate at room temperature. Their control can be achieved with microwave spin control and resonant optical excitation but is hindered by the broadening of optical transitions from thermal phonons and spectral diffusion. Furthermore, spin-qubit optical transitions are often outside the telecommunications wavelength band required for long-distance fiber optic transmission. Harnessing the coupling between mechanical degrees of freedom and spins has emerged as an alternative route for controlling spin-qubits. However, connecting spin-mechanical interfaces to optical links to realize a spin-photon interface has remained a challenge. Here we demonstrate such an interface using a diamond optomechanical cavity that does not depend on optical transitions and can be applied to a wide range of spin qubits.
Our device consists of a diamond microdisk resonator studied in [Optica 3, 963-970 (2016)]. The microdisk is fabricated from optical grade diamond that contains ensembles of NV centres. We use an optical mode at 1564 nm with the quality factor Qo = 150k. The mechanical mode which we use to couple to the NV spin state is a radial breathing mode with a frequency of around 2.1 GHz with the quality factor Qm = 4k. The device operates in the sideband resolved regime enabling optomechanical self-induced oscillations for sufficiently high optical input power of a blue detuned laser. These oscillations can produce the stress of a few MPa, large enough to drive the electronic spins of NV centers. We use a standard diamond NV confocal microscope to initialize and readout the NV state. The MW pulses transfer the population between |-1⟩<->|0⟩ and |+1⟩<->|0⟩ state. We wait for 0.7 us with the mechanical drive that drives the |-1⟩<->|+1⟩ transition. 
In our measurements, we observe a coinciding dip in the |+1⟩ population and a peak |-1⟩ population, that verifies that the spins are being optomechanically driven. On calibrating this signal with the MW Rabi contrast and the background signal, we estimate a driving rate of 2pix170kHz and ~45% transfer of spin population between |±1⟩ states. Feasible improvements in device geometry will increase the optomechanically-induced driving rate by a few orders of magnitude allowing for coherent control of NV spins using an optomechanical resonator.

technical paper

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Since the discovery of the Higgs boson at the LHC in 2012, no sign of new physics beyond the Standard Model has been found. The SUSY and exotic particles searches have not uncovered signs of new physics, as the model-dependent searches. In recent years, multiple unsupervised machine learning methods have been proposed to search for new physics at the LHC. This poster will explore the use of a variational auto-encoder (VAE) to perform a general search in proton-proton collisions at the LHC using large radius jets in ATLAS simulation data. To test our workflow, we trained the algorithm on low-level jet information to differentiate between the dominant QCD background and a chosen test signal corresponding to top quark jets. The most anomalous jets predicted by the VAE were selected to plot the invariant mass spectrum and to find the top quark mass peak. Our study found an important correlation between the jet invariant mass and the loss function of the VAE, resulting in a sculpting of our background and preventing the apparition of the top peak. We successfully used a mass-decorrelation method based on Outlier Exposure to prevent this sculpting.

Search for New Physics Inside Boosted Jets at the ATLAS Detector Using Anomaly Detection

Telescope Array experiment has recorded several short time bursts of air shower like events. These bursts are very distinct from conventional single showers, and are found to be strongly correlated with lightnings. We proposed these bursts represent the direct manifestation of the dark matter annihilation events within the so-called axion quark nugget model. We discuss how to test this proposal by searching for the radio signals in frequency band (0.5−200) MHz which must be synchronized with the Telescope Array bursts.

Dark matter, axion quark nugget, and mysterious bursts observed by telescope array

Longstanding evidence from observational astronomy indicates that non-luminous "dark matter" constitutes the majority of all matter in the universe, yet this mysterious form of matter continues to elude experimental detection. The study presented in this talk is part of an ongoing programme to search for dark matter production in high-energy proton-proton collisions at the Large Hadron Collider (LHC) at CERN. This search targets a model in which dark matter is produced in association with the emission of a hypothesized heavy Higgs boson in the dark sector, which then decays to a pair of W bosons. The final-state signature of this model would be an excess of missing transverse energy in the detector due to undetected dark matter production, along with two reconstructed W bosons. A search was recently performed targeting this final state in the 'hadronic' decay channel, wherein both W bosons decay to a pair of quarks. The semi-leptonic WW decay channel, in which one of the bosons instead decays to a lepton and neutrino, will complement and extend the reach of the existing search in the hadronic channel. A dark matter search in this semi-leptonic WW decay channel is presented.

Search for Dark Matter Produced in Association with a Dark Sector Higgs Boson in Proton-Proton Collisions with the ATLAS Detector

DEAP-3600 is a liquid argon detector designed to directly detect dark matter by searching for nuclear recoil (NR) events caused by elastically scattered weakly interacting massive particles, a prime candidate for dark matter. Pulse-shape discrimination properties of the argon allow for significant separation between electromagnetic recoil (ER) events and NR events. The majority of the events in the ER spectrum are beta decays of Ar-39, which is an isotope naturally present in argon. Several efforts are underway to study the Ar-39 spectrum in DEAP-3600. In order to perform these studies, we must have an extensive understanding of the possible background in the ER spectrum. A possible background contribution to this spectrum are events from Kr-85, a radioactive isotope that can potentially bypass the purification methods used to fill the detector with argon. Trace amounts of Kr-85 are produced in the atmosphere via interactions with cosmic rays and Kr-84, which could be present in atmospheric argon. Given that the beta spectrum endpoint (Q-value) of Kr-85 is slightly higher than Ar-39, excess events in the region just above the Q-value of Ar-39 are expected if there is any contamination by Kr-85. A full spectrum fit was done to search for potential contributions from this isotope.

Constraining contributions from Kr-85 in DEAP-3600

The Cryogenic Underground TEst Facility (CUTE) is fully operational underground at SNOLAB. The facility can host up to six of the next generation SuperCDMS cryogenic detectors, and allows for the opportunity to search for low-mass dark matter while testing the new detectors. The SNOLAB cleanroom laboratory provides a low-background and low-cosmogenic-activation environment for CUTE operations. Estimating the background from radioactive processes with Geant4 simulations becomes a crucial task in informing the background budget for the experiment. This presentation will describe the radioactive background characterization of the CUTE facility, and discuss its validation through comparison with acquired data.

Radioactive Background Characterization of the Cryogenic Underground TEst Facility (CUTE)

We propose an efficient, nanoplasmonic method to selectively enhance the spontaneous emission rate of a quantum system by changing the polarization of an incident control field, and exploiting the polarization dependence of the system's spontaneous emission rate. This differs from the usual Purcell enhancement of spontaneous emission rates as it can be selectively turned on and off. Using a three-level system in a quantum dot placed in-between two silver nanoparticles and a linearly-polarized, monochromatic driving field, we present a protocol for rapid quantum state initialization; while maintaining long coherence times for control operations. This process increases the overall amount of time that a quantum system can be effectively utilized for quantum operations, and presents a key advance in quantum computing.

Polarization control of spontaneous emission for rapid quantum state initialization

Single acceptor dopants in Si along with dangling bonds are enabling technologies for atomic scale charge and spin-based devices.[1] Additionally, recent advances in hydrogen lithography have enabled the patterning of quantum dot based circuit elements with atomic precision.[2] We engineered a single acceptor coupled to a dangling bond wire on highly doped p-type H-Si(100) and characterized its electronic properties with scanning tunneling spectroscopy. The coupled entity has an electronic structure that behaves as a conductive wire from which the charge state of the dopant can be accessed and has a complex dependence on the dangling bond wire length. In addition, dI/dV mapping reveals features reminiscent of charging rings that are centered over the dopant and overlap with the wire.[3] This overlap varies with electric field and its tunability may augment the functionality of dangling bond based quantum devices.

References:
[1] A. Laucht et al., "Roadmap on quantum nanotechnologies", Nanotechnology, vol. 32, no. 16, p. 162003, 2021. Available: 10.1088/1361-6528/abb333 
[2] T. Huff et al., "Binary atomic silicon logic", Nature Electronics, vol. 1, no. 12, pp. 636-643, 2018. Available: 10.1038/s41928-018-0180-3
[3] N. Turek, S. Godey, D. Deresmes and T. Mélin, "Ring charging of a single silicon dangling bond imaged by noncontact atomic force microscopy", Physical Review B, vol. 102, no. 23, 2020. Available: 10.1103/physrevb.102.235433 

![Figure 1. a) (1.8 V 50 pA) STM image of a 7 dangling bond wire fabricated next to a subsurface Boron dopant on highly doped P type H-Si (100) with individual spectroscopy points denoted by arrows. b) dI/dV spectroscopy taken over the dopant and wire shown in a), exhibiting previously unobserved peaks at -1.4 V and 0.9 V.][1]


[1]: https://i.ibb.co/X355XS2/fig1.png

Towards the atomic scale readout of single acceptor states in p-doped Si

In the past 20 years, large-scale datasets of cell phone traces have emerged as a key proxy to study human movement patterns, and how those patterns change in response to exogenous events such as natural disasters or terrorist attacks. These data have proven especially useful to understand the effects of public policy in the current COVID-19 pandemic, where "lockdowns" and other mobility-based restrictions have served as the main intervention deployed by governments in the absence of a vaccine. In this talk, I will give an overview of how tools from information theory and statistical physics have been applied to high-resolution mobile phone data to understand the (in)effectiveness of physical distancing measures in reducing human mobility over the past year. In particular, I will discuss our own efforts to quantify heterogenity in human contact patterns and so-called "superspreading events"--both outsize drivers of epidemic spread.

Statistical Physics & Human Mobility in COVID-19

We numerically analyze the spectrum of the Laplacian on the moduli space of a genus zero Riemann surface with four punctures via a perturbative expansion of the path integral of Liouville theory. Our results furnish evidence that the eigenvalues obey the statistics of a random matrix in the Gaussian Orthogonal Ensemble. We comment on possible implications for the quantum geometry of Riemann surfaces and quantum gravity in anti–de Sitter space. Based on work with A. Maloney and T. Numasawa.

Chaos and the spectrum on Moduli space

The state of a quantum system evolves according to the Schrödinger equation. Often, one is interested in the behaviour of parts of a whole system only. Such parts are called open quantum systems, as they exchange energy, matter, information with their surroundings. The dynamics of open systems is very complicated. They are a central topic of research in many theoretical and applied fields of modern quantum theory, such as quantum optics and quantum information, having applications to other sciences (chemistry, biology). One of the main tools for the analysis is the Markovian approximation, in which the open system dynamics is approximated by the so-called master equation. In some aspects, the latter is akin to the Schrödinger equation, in others it is crucially different due to the open nature of the system. Despite the ubiquitous use of the Markovian approximation, its rigorous justification turns out to be a difficult task.
In this talk we explain recent ideas and results of a mathematical approach proving the validity of the Markovian approximation, i.e., of the master equation. The talk does not require the listeners to have a deep background in quantum theory and should be accessible to a rather general audience.

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Optomechanical interface between telecom photons and spin quantum memory

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