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Applied Physics / Physics Colloquium

Applied Physics/Physics Colloquium presents "Quantum Sensing of Quantum Materials"

Topic: 
Quantum Sensing of Quantum Materials
Abstract / Description: 

The magnetic fields generated by spins and currents provide a unique window into the physics of correlated-electron materials and devices. Proposed only a decade ago, magnetometry based on the electron spin of nitrogen-vacancy (NV) defects in diamond is emerging as a platform that is exceptionally suited for probing condensed matter systems: it can be operated from cryogenic temperatures to above room temperature, has a dynamic range spanning from DC to GHz, and allows sensor-sample distances as small as a few nanometers. As such, NV magnetometry provides access to static and dynamic magnetic and electronic phenomena with nanoscale spatial resolution. While pioneering work focused on proof-of-principle demonstrations of its nanoscale imaging resolution and magnetic field sensitivity, now experiments are starting to probe the correlated-electron physics of magnets and superconductors and to explore the current distributions in low-dimensional materials. In this talk, I will review some of our recent work that uses NV center magnetometry to image skyrmions in thin magnetic films, measure the spin chemical potential in magnetic insulators, and image hydrodynamic electron flow in graphene.

 


Winter Qtr. Colloq. committee: M. Schleier-Smith (Chair), B. Cabrera, S. Dimopoulos, T. Heinz, S. Kachru & L. Tompkins
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, January 7, 2020 - 4:30pm
Venue: 
Hewlett 200

AP 483 Seminar Series presents "Photovoltaic Restoration of Sight in Retinal Degeneration"

Topic: 
Photovoltaic Restoration of Sight in Retinal Degeneration
Abstract / Description: 

Retinal degenerative diseases lead to blindness due to loss of the “image capturing” photoreceptors, while neurons in the “image-processing” inner retinal layers are relatively well-preserved. Information can be reintroduced into the visual system by photovoltaic subretinal implants, which convert incident light into electric current and stimulate the secondary retinal neurons.

 

To provide sufficient light intensity for photovoltaic stimulation while avoiding visual perception by remaining photoreceptors, images captured by a camera are projected onto the retina from augmented-reality glasses using pulsed near-infrared light. This design avoids the use of bulky electronics and wiring, thereby greatly reducing the surgical complexity and enabling scaling the number of photovoltaic pixels to thousands. Many features of the natural retinal signal processing are preserved in this approach, and spatial resolution matches the pixel pitch (so far 100 μm pixels in human patients, and 50 μm in rodents). For a broad acceptance of this technology by patients who lost central vision due to Age-Related Macular Degeneration, visual acuity should exceed 20/100, which requires pixels smaller than 25 μm. I will present a 3-dimensional electro-neural interface scalable to cellular dimensions and discuss the outlook and challenges for future developments.


 AP483 Optics and Electronics Seminar Series 2019-20 (Sponsored by Ginzton Laboratory, SPRC, Applied Physics, Physics, and HEPL).

Date and Time: 
Monday, February 24, 2020 - 4:15pm
Venue: 
Spilker 232

AP 483 Seminar Series presents "Taking the Humble FBG on a Voyage of Discovery from the Lab Bench to the Hospital and Beyond"

Topic: 
Taking the Humble FBG on a Voyage of Discovery from the Lab Bench to the Hospital and Beyond
Abstract / Description: 

Fiber Bragg gratings (FBGs) emerged almost magically in 1978. Since then, they have developed from being primarily of academic interest, to being one of the most versatile photonic components for both telecommunications and sensing. 

I was lucky enough to get introduced to photonics during the early years of discovery and experimentation with FBGs and ended up making FBG components for telecommunications. Jumping forward a few decades, I had moved away from telecommunications and had started to dabble with free space optical sensing. Then, during a chance meeting over a beer in Sydney, I was asked, rather naively, if it was possible to use optical fiber to monitor what goes on in the esophagus when we swallow. This set me off on an entirely new path and, pulling together some ideas from telecoms, and some basic mechanical engineering, my team ended up developing a range of sensors for monitoring pressure in the human digestive tract. 

Being able to detect swallowing disorders quickly led to monitoring in other regions of the gut, like the colon and small bowel, and, together with colleagues from Flinders Medical Center, we provided some details of the inner workings of the human gastrointestinal tract. Thus, the fiber optic catheter was born. This device kept me busy for almost 10 years, during which time we worked closely with clinical research groups to write a whole new chapter on how the gut works.

The next ‘Eureka’ moment came when we had to develop a temperature independent version of our sensor, initially for monitoring pressure beneath bandages. The very simple design that resulted worked well for sub-bandage measurements but has also become a key technology that has moved to applications in aerospace, pipeline monitoring, and mining.

When I started working in optics, I never thought I'd end up monitoring what makes your stomach growl when hungry, how air flows across an airplane wing, or detecting pressure transients in water pipes. 

During this talk I will explain how our basic transducers work and will then describe the applications they are now being applied to, demonstrating how the humble FBG has opened up the scope and reach of fiber-optic sensing.


 

AP483 Optics and Electronics Seminar Series 2019-20 (Sponsored by Ginzton Laboratory, SPRC, Applied Physics, Physics, and HEPL).

Date and Time: 
Monday, February 10, 2020 - 4:15pm
Venue: 
Spilker 232

AP 483 Seminar Series presents "Non-Hermitian Photonics: Optics at an Exceptional Point"

Topic: 
Non-Hermitian Photonics: Optics at an Exceptional Point
Abstract / Description: 

In recent years, non-Hermitian degeneracies, also known as exceptional points (EPs), have emerged as a new paradigm for engineering the response of optical systems. At such points, an N-dimensional space can be represented by a single eigenvalue and one eigenvector. As a result, these points are associated with abrupt phase transitions in parameter space. Among many different non-conservative photonic configurations, parity-time (PT) symmetric systems are of particular interest since they provide a powerful platform to explore, and consequently utilize, the physics of exceptional points in a systematic manner. In this talk, I will review some of our recent works in the area of non-Hermitian (mainly PT-symmetric) active photonics. For example, in a series of works, we have demonstrated how the generation and judicial utilization of these points in laser systems can result in unexpected dynamics, unusual linewidth behavior, and improved modal response. On the other hand, biasing a photonic system at an exceptional point can lead to orders of magnitude enhancement in sensitivity, an effect that may enable a new generation of ultrasensitive optical sensors on-chip. Non-Hermiticity can also be used as a means to promote or single out an edge mode in photonic topological insulator lattices. Rotation sensors play a crucial role in a diverse set of applications associated with navigation, positioning, and inertial sensing. Most optical gyroscopes rely on the Sagnac effect induced phase shift that scales linearly with the rotational velocity. In ring laser gyroscopes (RLGs), this shift manifests itself as a resonance splitting in the emission spectrum that can be detected as a beat frequency. The need for evermore precise RLGs has fueled research activities towards devising new approaches aimed to boost the sensitivity beyond what is dictated by geometrical constraints. In this respect, attempts have been made in the past to use either dispersive or nonlinear effects. Here, we propose a new scheme for ultrasensitive laser gyroscopes that utilizes the physics of exceptional points. By exploiting the properties of such non- Hermitian degeneracies, we show that the rotation-induced frequency splitting becomes proportional to the square root of the gyration speed, thus enhancing the sensitivity to low angular rotations by orders of magnitudes. We will then describe a possible modification of a standard RLG to support an exceptional point and measure the resulting enhanced sensitivity in the proposed system.


 

Date and Time: 
Monday, January 27, 2020 - 4:15pm
Venue: 
Spilker 232

AP 483 Seminar Series presents "Where Are We Heading: A Brief History and Future of Navigation"

Topic: 
Where Are We Heading: A Brief History and Future of Navigation
Abstract / Description: 

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AP483 Optics and Electronics Seminar Series 2019-20 (Sponsored by Ginzton Laboratory, SPRC, Applied Physics, Physics, and HEPL).

Date and Time: 
Monday, January 13, 2020 - 4:15pm
Venue: 
Spilker 232

AP 483 & AMO Seminar Series presents "Quantum Acceleration of Electromagnetic Axion Searches"

Topic: 
Quantum Acceleration of Electromagnetic Axion Searches
Abstract / Description: 

The QCD axion, which solves the strong CP problem in QCD, is one of the best motivated dark-matter candidates. I will discuss efforts to develop electromagnetic searches for QCD axion dark matter with masses below 1 micro-eV, including the Dark Matter Radio Cubic Meter experiment, which will probe the QCD axion band over 1.5 orders of magnitude in axion mass. However, full coverage of the QCD axion band will not be possible without acceleration by using quantum measurement techniques, which can be used to evade the standard quantum limit by the exploitation of quantum correlations in the electromagnetic signals. While photon counting is a useful technique to evade the SQL at masses above 1 micro-eV, it is not a useful technique at lower mass ranges. I will describe Quantum Upconverters, which convert signals from DC up to ~300 MHz to the microwave frequency range. Quantum upconverters can be used to implement techniques including backaction evasion to outperform the Standard Quantum Limit at the RF frequencies probed by DM Radio. They can also be used to improve electromagnetic sensing of nuclear spins for NMR-based detection schemes (including CASPEr).

(This seminar series is sponsored by Ginzton Laboratory, SPRC, Applied Physics, Physics, and HEPL)

Date and Time: 
Monday, March 2, 2020 - 4:15pm
Venue: 
Spilker 232

AP 483 & AMO Seminar Series presents "Quantum Electron Microscopy"

Topic: 
Quantum Electron Microscopy
Abstract / Description: 

Of the wide variety of sophisticated techniques employed in optical microscopy, of special interest to physicists are schemes which use quantum correlations to increase sensitivity beyond the classical limit. Such technology would be especially applicable in transmission electron microscopy (TEM) since the image resolution of samples of critical interest (e.g. proteins, polymers, and battery materials) is limited by beam damage. However, in contrast to the fantastic diversity and modularity of light optics, electron optics are significantly constrained. I will describe our project of developing new electron optics to enable dose-efficient TEM. While quantum metrology is generally associated with an entangled probe (which has not yet been demonstrated with freespace electrons), it is also possible to perform quantum-optimal measurements with a single particle using sequential measurements [1]. In fact, it is possible to gain significant information about absorbing samples using only damage-free counterfactual measurements [2]. More typically, TEM samples are phase objects. We have shown that an approach called Multi-Pass TEM (MPTEM) can reduce damage by an order of magnitude for realistic samples [3]. The key new electron optics of the MPTEM are the switchable mirrors, which trap electrons in a cavity where the sample is re-imaged multiple times. We are currently building a 10 keV MPTEM [4] as a proof of concept. [1] Quantum Metrology, Vittorio Giovannetti, Seth Lloyd, and Lorenzo Maccone (2006). [2] Designs for a Quantum Electron Microscope, P. Kruit et al, Ultramicroscopy (2016). [3] Multi-Pass Transmission Electron Microscopy, T. Juffmann et al, Scientific Reports (2017). [4] Design for a 10 keV Multi-Pass Transmission Electron Microscope, S. A. Koppell, Ultramicroscopy (2019).

Date and Time: 
Monday, January 6, 2020 - 4:15pm
Venue: 
Spilker 232

Applied Physics/Physics Colloquium presents “The Future of Particle Physics”

Topic: 
The Future of Particle Physics
Abstract / Description: 

High energy particle physics has the ambitious goals of uncovering the most fundamental constituents of reality and deciphering the rules by which those constituents interact, both today and in the first instants of the Big Bang. Our ability to construct higher and higher energy particle accelerators does not scale well with these ambitions, so progress here will increasingly depend on global collaboration and being smarter with the data that we have in hand.
Beyond colliders, the future of this field will increasingly rely on three other approaches that I will describe:
— Transformational advances in the sensitivities and capabilities of sensors to detect feebly interacting particles such as dark matter and neutrinos.
— Increasing our access to extreme environments provided by Nature, such as supernovae, black hole mergers, and the echoes of the Big Bang.
— Using theory to map fundamental questions seemingly out of experimental reach, e.g. the nature of quantum gravity and spacetime, into quantum systems and simulations that can be created and studied in the laboratory.


 

Aut. Qtr. Colloq. committee: R. Blandford (Chair), B. Feldman, A. Kapitulnik, B. Lev and V. Khemani

Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, November 19, 2019 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium presents "The Physics and Astrophysics of Black Holes and Horizons"

Topic: 
The Physics and Astrophysics of Black Holes and Horizons
Abstract / Description: 

One of the most striking predictions of the general theory of relativity is the formation of black hole and cosmic horizons sequestering different regions of spacetime. In this talk we will overview recent theoretical and observational developments in this area. At the classical and quantum level, radiation plays an important role in observations and thought experiments. Hawking's result that black holes radiate raises serious puzzles, while its analogue in early universe cosmology yields a successful quantum theory of the origin of structure. The pursuit of a complete theory of quantum gravity has led to qualitatively new lessons about emergent spacetime structure in the presence of horizons. Turning to observations, the proposition that black holes with masses from three to ten billion times that of the sun are quite common in the universe grew from a conjecture to a conviction. Recent observations using the Fermi Gamma-ray Space Telescope, LIGO/VIRGO and the Event Horizon Telescope have validated general relativity and demonstrated how black holes are born, how they affect their surroundings and how they power the most luminous cosmic sources.


 

Aut. Qtr. Colloq. committee: R. Blandford (Chair), B. Feldman, A. Kapitulnik, B. Lev and V. Khemani
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, November 12, 2019 - 4:30pm
Venue: 
Hewlett 200

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