Seminars are Wednesdays, 11:00AM–12 NOON

Haus Room, 36-428 (*unless otherwise noted)

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# Fall 2018

##### September 12: Dr. Andrew R. Lupini

Oakridge National Laboratory

**Imaging and Controlling Single Atoms with an Electron Beam**

Abstract: Since the invention of the electron microscope the imaging resolution has traditionally been limited by the aberrations of the electron lenses. Fifty years after the first proposal outlining how to correct these imperfections, modern aberration-correctors have become widespread across many laboratories. Computer control with rapid feedback to measure and correct the controls forms an important part of these systems, and advanced methods to interpret and process the rich information stream from these instruments present numerous exciting challenges.

Over the last few years, electron microscopy has started to undergo a transition from merely being used as an imaging device to a tool capable of addressing and in some cases even control single atoms. In his famous talk, There’s Plenty of Room at the Bottom, Richard Feynman highlighted both the benefits of improving the resolution of the electron microscope and the potential applications of writing or controlling single atoms. Recent work has begun to demonstrate the feasibility of manipulating single atoms in 2D materials, however given the ubiquitous use of silicon in modern electronics, there remains a need to achieve this feat inside 3D crystals technologically relevant materials. In this talk I will show some of the progress towards these goals and demonstrate using the electron beam to control dopant atoms one-by-one inside a semiconductor crystal.

Dr. Lupini obtained his Ph.D. in Physics from the Cavendish Laboratory of Cambridge University in the UK, under the supervision of Dr. Andrew Bleloch, in 2001. Dr. Lupini is one of the inventors of the first aberration-corrector in a scanning transmission electron microscope to demonstrate an improved resolution. He is currently a R&D staff member in the Materials Science and Technology Division of Oak Ridge National Laboratory in Tennessee. His research interests include all forms of electron microscopy and spectroscopy, especially as applied to new or quantum materials.

11am

Haus Room, 36-428

##### September 26: Jean-Philippe MacLean

University of Waterloo

**Direct characterization of ultrafast energy-time entangled photon pairs**

Abstract: In the famous example suggested by Einstein, Podolsky and Rosen (EPR), two particles can be highly correlated in position and momentum. For photons, strong EPR-like correlations can also occur in the energy-time degree of freedom, that is, between the frequency and the time of arrival of the photons. This type of entanglement enables fundamentally quantum effects such as dispersion cancellation and clock synchronization. However, detection of this entanglement and observation of these effects can require ultrafast time resolution beyond the capabilities of current photon detectors. Thus, for operations on ultrafast timescales, more powerful and complex methods are required.

We use a nonlinear technique known as optical gating to surpass the limitations in current detectors and achieve subpicosecond time resolution for single photon pairs. Optical gating in conjunction with single photon spectrometers then enables us to measure both the spectral and temporal correlations of a two-photon state, allowing us to observe for the first time EPR correlation but in frequency and in time.

Jean-Philippe is originally from Montreal. He completed his undergraduate in Physics at McGill University in 2013. During his undergraduate, he worked on high-intensity ultrafast optics at the INRS in Varennes and then moved to quantum optics for PhD at the University of Waterloo.

11am

Haus Room, 36-428

##### October 10: Ken Segall

Colgate University

**Think Super: Artificial Neurons made from Superconductors**

Abstract: Our research focuses on the design, fabrication and testing of integrated circuits which can simulate neuron spiking dynamics on very fast timescales in a biologically realistic way [1]. These circuits are based on a low-temperature, superconducting electronics technology (Josephson junctions) that has already been successful in creating ultra-sensitive magnetometers, superconducting qubits, high-performance radiation detectors, high-speed digital processors, and the primary voltage standard in the U.S. The short spiking times in these artificial neurons combined with analog scaling properties give this approach a potentially unprecedented ability to investigate long term dynamics of large networks [1]. In addition, these artificial neurons dissipate almost no power, making them a candidate for a low-power, neuromorphic computing technology.

We have performed the first experiments on two superconducting neurons which are mutually coupled with artificial axons and synapses [2,3]. In some regions of parameter space the neurons are desynchronized. In others, the Josephson neurons synchronize in one of two states, in-phase or anti-phase. An experimental alteration of the delay and strength of the connecting synapses can toggle the system back and forth in a phase-flip bifurcation, which is a biologically-realistic phenomenon [4] Firing synchronization states are calculated >70,000 times faster than conventional digital approaches. With their speed and low energy dissipation (10-17 Joules/spike), this set of proof-of-concept experiments establishes Josephson junction neurons as a viable approach for improvements in neuronal computation as well as applications in neuromorphic computing.

1 P. Crotty, D. Schult, and K. Segall, Phys Rev E. 82 (2010).

2 K. Segall, S. Guo, P. Crotty, D. Schult, and M. Miller, Physica B 455, 71 (2014).

3 K. Segall, M. LeGro, S. Kaplan, O. Svitelskiy, S. Khadka, P. Crotty, and D. Schult, Phys Rev E. 95 (2017).

4 N. M. Dotson and C. M. Gray, Phys Rev E. 94 (2016).

##### October 24: Thomas Ohki

Raytheon BBN Technologies

**Enabling Technology for Beyond Intermediate Scale Quantum Computing Systems**

Abstract: The goal of implementing of a cryptologically meaningful quantum computing system requires not only advances in physical qubit performance and fault tolerant operation but almost an equally hard problem of engineering an achievable system. This requires the ability to grow to large numbers of qubits while incorporating new scalable technologies as the total system size and complexity also grows. For quantum computing systems, significant advances and demonstrations can be made at small to moderate scales enabled by “brute force” methodologies. One of my focuses has been to understand what gaps may exist in the near future for these systems and to start advancing these immature enabling technologies. Whether this is novel cryogenic microwave components, control and readout electronics or novel materials, each advance has its own relevance in the timeline of a large scale system. Balancing the demand vs readiness for a capability can be a complicated dance between physicist and engineers, government mission roadmaps and commercial market expectations. We show progress toward some of these enabling technologies areas for quantum information systems.

Bio: Lead of the Quantum Engineering and Computing group at Raytheon BBN Technologies which is focused on development and applications of superconducting devices for quantum information, microwave systems and beyond CMOS digital technologies. Active research areas include superconducting quantum and classical computing, as well as superconducting devices hybridized with spintronic and 2-D materials. He has built a world class quantum computing research laboratory in Cambridge Massachusetts and superconducting device fabrication capabilities at Raytheon.

##### October 31: Mahdi Naghiloo

Washington University, St. Louis

**Optimal precision in frequency estimation using a quantum bit**

Abstract: In quantum metrology, one seeks to take advantage of quantum properties to maximally utilize the available measurement resources. For parallel resources, such as the number of quantum systems, entanglement can be utilized to achieve Heisenberg scaling. Similarly, one can also utilize quantum coherences to optimally exploit the serial resource, time. We demonstrate how quantum coherence can be optimally harnessed through coherent control to expedite a frequency estimation task. In our experiment, an unknown external oscillating signal causes the quantum system to undergo periodic changes. By applying quantum pulses on top of the oscillating signal, the state of the system could be controlled so that the final readout of the quantum system became highly sensitive to the precise value of the oscillation frequency. The underlying physical source of the advantage is related to the fact that the energy of the quantum system is time-dependent, which causes the quantum states corresponding to different frequencies to accelerate away from each other, giving enhanced distinguishability in a given time. This result demonstrates a fundamental quantum advantage for frequency estimation.

##### December 12: Vinod Menon

City University of New York (CUNY)

**Control of Light-matter Interaction in 2D Materials**

Abstract: Two-dimensional (2D) Van der Waals materials have emerged as a very attractive class of optoelectronic material due to the unprecedented strength in its interaction with light. In this talk I will discuss approaches to enhance and control this interaction by integrating these 2D materials with microcavities, and metamaterials. I will first discuss the formation of strongly coupled half-light half-matter quasiparticles (microcavity polaritons) [1] and their spin-optic control [2] in the 2D transition metal dichacogenide (TMD) systems. Prospects of realizing condensation and few photon nonlinear switches using Rydberg states in TMDs will also be discussed. Following this, I will discuss the routing of valley excitons in 2D TMDs using chiral metasurfaces [3]. Finally, I will talk about room temperature single photon emission from hexagonal boron nitride [4] and the prospects of developing deterministic quantum emitters using them [5].

References:

[1] X. Liu, et al., Nature Photonics 9, 30 (2015)

[2] Z. Sun et al., Nature Photonics 11, 491 (2017)

[3] S. Guddala et al., ArXiv 1811.00071

[4] Z. Shotan, et al., ACS Photonics 3, 2490 (2016)

[5] N. Proscia, et al. Optica 5, 1128 (2018).

Bio: Vinod Menon is a Professor of Physics at the City College and Graduate Center of the City University of New York (CUNY). He is also an IEEE Distinguished Lecturer in Photonics (2018-19). He joined CUNY in fall 2004 as part of the initiative in photonics. Prior to joining CUNY he was at Princeton University (2001-2004) where he was the Lucent Bell Labs Post-Doctoral Fellow in Photonics. He received his MSc in Physics (Quantum Optics specialization) from the University of Hyderabad, India in 1995 and his Ph.D. in Physics from the University of Massachusetts in 2001. His current research interests include cavity QED with two-dimensional semiconductors, controlling transport and energetics in organic molecules through strong light-matter coupling, and engineered nonlinear optical materials. More details about his group can be found at www.lanmp.org

##### Jan 30: Dr. Jelmer Renema

University of Twente, the Netherlands

**The Hardness of Boson Sampling with Imperfections**

Abstract: The next milestone in experimental quantum information processing is the demonstration of a quantum advantage, i.e. the unambiguous demonstration of an information processing task, no matter how trivial, at which a quantum device outperforms a classical computer. This is possible using photonics, where it involves sending single photons through a random unitary network and drawing samples from the output in the photon number basis. This is known as boson sampling.

A major practical hurdle on the way to constructing a boson sampler is that it is poorly understood how imperfections in the system, such as photon loss and finite distinguishability (wave function overlap) degrade the hardness of simulating the quantum interference occurring in such a device.

In this talk, I will address this problem by demonstrating a classical algorithm which uses these two imperfections to perform an efficient classical simulation of a boson sampler. In the limit of large numbers of photons, this algorithm is efficient in the number of photons for any nonzero level of imperfections, which shows that the equivalent of an error threshold for boson sampling does not exist.

Furthermore, by considering a fixed number of photons, we can demarcate those areas of the parameter space where a quantum advantage demonstration using photonics is ruled out. This algorithm can therefore be used to guide the design of future photonic quantum advantage demonstrations. I will show that strong qualitative improvements to photonics technology are needed to demonstrate a quantum advantage using photonics.

Bio: Dr. Jelmer Renema is currently a Veni Fellow with Pepijn Pinkse at the University of Twente, working on multiphoton quantum optics and the quantum optics of scattering media. He is also the CTO of QuiX B.V., a photonic quantum technologies company. Previously, he was a Junior Research Fellow at the University of Oxford, with Ian Walmsley, working on integrated quantum optics. Before that, he obtained his PhD on the detection mechanism of nanowire superconducting single photon detectors in the group of Dirk Bouwmeester and Martin van Exter in Leiden.

11am

Haus Room, 36-428

##### Feb 6: Adrian Menssen1

University of Oxford

**Interfering Distinguishable Photons: Understanding Three and Four Photon Interference**

Abstract: Quantum interference of two independent photons in pure quantum states is fully described by the particles’ distinguishability: the closer the particles are to being identical, the higher the degree of quantum interference. When more than two particles are involved, the situation becomes more complex and interference capability extends beyond pairwise distinguishability. We study many-particle interference in three and four photons in a series of experiments. We show that for three photons the three distinct distinguishabilities between pairs of photons are not sufficient to fully describe the photons’ behaviour in a scattering process, but that additionally a fourth parameter, a collective phase, governs the scattering process. Furthermore, we experimentally demonstrate that surprisingly four photons can interfere even when they are pair-wise orthogonal. We illustrate these effects in a graph theoretical picture we developed.

11am

Haus Room, 36-428

##### April 11: Kaoru Minoshima

University of Electro-Communications (Tokyo, Japan)

**Intelligent Optical Synthesizers:Versatile control of optical waves enables studies from molecular physics to astronomy**

4pm

2019 Hermann Anton Haus Lecture

Haus Room, 36-428

Reception at 5pm

Fourth Floor, Building 32

Image credit: Greg Steinbrecher