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Quantum confinement and manipulation of charge carriers are critical for achieving devices practical for various quantum technologies such as quantum sensing. Atomically thin transition metal dichalcogenides (TMDCs) have attractive properties such as spin-valley locking, large spin-orbit coupling and high confinement energies which provide a promising platform for novel quantum technologies. In this talk, we present the design and fabrication of electrostatically gated quantum structures based on fully encapsulated monolayer tungsten diselenide (WSe2) aimed at probing and measuring the properties of the confined single and few-hole states in these structures. Furthermore, we successfully demonstrate that local control gates successfully pinch-off the current across the device with gate voltages consistent with their lithographic widths. Finally, we discuss the origins of the observed mesoscopic transport features related to the quantum dots through the WSe2 channel.

2021 CAP Virtual Congress

Gated quantum dots in van der Waals materials

transition metal dichalcogenide

gated quantum dots

van der waals heterostructure

2d materials

transport

**WELCOME TO THE 2021 CAP VIRTUAL CONGRESS UNDERLINE PLATFORM**

The CAP staff and our organizing and program committees are pleased to welcome you to our 2021 Congress filled with plenary talks, technical sessions/talks, student presentations and competition sessions, workshops, and several symposia offered by the CAP divisions and its partners.  

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Registered delegates should use the schedule button to call up the details of the session/event they wish to attend.  Each sessions includes a link to access the online platform where the event is taking place, either within Underline or through other Congress-related Zoom meetings.  

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We look forward to sharing this exciting week with you!


technical paper

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

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

In microscopy, the imaging of light-sensitive materials has been a persistent problem, as the sample being studied may be altered or damaged by the illumination itself. Naturally, to overcome over-illuminating the sample, one can reduce the intensity of the classical light source; however, reducing the source intensity comes with a trade-off which affects noise and image quality. In recent years, it has been shown that using quantum illumination as a source for imaging schemes significantly reduces photon illumination of the sample while maintaining image quality. In fact, in our previous work [1] we combine two quantum imaging and detection schemes in a technique coined “Interaction-free-ghost-imaging” and achieve results with low photon number and high contrast images. 
A further limitation of all direct imaging schemes, whether they be quantum or classical, is the so-called diffraction limit. When measuring intensity directly, the maximal resolution is dictated by the size of optical apertures in the imaging system. Recent results [2] [3] have shown that performing phase-sensitive measurements, as opposed to intensity measurements, could increase resolution by several orders of magnitude. 
We propose an experiment implementing the super-resolution technique in a quantum ghost-imaging scheme. We aim to show that the added benefits of low photon counts along with increased resolution show promise for imaging small light-sensitive objects such as biological cells, and further challenges the notion of how many photons are needed to form a visible image.

[1] Zhang,Y., Sit, A., Bouchard, F., Larocque, H., Grenapin, F., Cohen, E., Elitzur, A., Harden, J. Boyd,R., Karimi, E, “Interaction-free-ghost-imaging of structured objects”, Optics Express 27, 2212-2224 (2019). 
[2] Tsang, M., Nair, R., Lu X, “Quantum Theory of Superresolution for two Incoherent Optical Point Sources”, Physical Review X 6, 031033 (2016). 
[3] Tham, W., Ferretti, H., Steinberg, A, “Beating Rayeigh’s curse by Imaging Using Phase”, Physical Review Letters 118, 070801 (2017).

Super-resolution Ghost-Imaging

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.

Optomechanical interface between telecom photons and spin quantum memory

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.

Gated quantum dots in van der Waals materials

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