Groups | Seminars || Courses | Outreach

Seminars

Seminars will be held held at room S-141 in the Physics and Astronomy Department building on Mondays at 4:00 PM, unless noted otherwise.

Fall 2019

September 9, 2019 Dr. Abijith Kowligy NIST, Boulder Mid-infrared frequency combs in the time-domain: single-cycle waveforms and quantum-noise-limited measurement (Host Tom Allison

We describe the generation of mid-infrared frequency combs across 3-27 micron using intra-pulse difference-frequency generation in quadratic nonlinear crystals. The frequency combs correspond to phase-stable, few-cycle pulse trains in the time-domain, and we demonstrate controllable carrier-envelope phase for these reproducible waveforms exhibiting <15-mrad phase-stability over several-hour time-scales. The radiation is characterized by dual frequency comb electro-optic sampling (EOS), which allows for direct, shot-noise-limited detection of the electric fields at room-temperature using commonplace near-infrared photodetectors at video refresh rates. The combination of low-noise sources and quantum-noise-limited measurement provides a route to explore intrinsic quantum noise at ultrafast time-scales, and we discuss initial results.

September 23, 2019 Prof. Dylan Yost Colorado State University Precision Laser Spectroscopy of Hydrogen (Host:Tom Allison)

Hydrogen is the most abundant element in the universe, and the most important element for the development of modern physics – an attribute that can be traced back to its simplicity as an effective two-body system. Currently, precision hydrogen spectroscopy remains an exciting field which determines the Rydberg constant, stringently tests QED, and measures the RMS charge radius of the proton and deuteron.  In addition, the techniques used to study hydrogen can often be transferred to other simple (i.e. two-body) atomic systems such as muonium or anti-hydrogen, which provide important tests for Beyond-Standard-Model physics.  Unfortunately, precision spectroscopy of simple atoms, while compelling, is also notoriously difficult due to the short-wavelength and high-power lasers required. In this talk, I will present our novel laser infrastructure, which allows for high precision spectroscopy of hydrogen and other simple atoms.  In addition, I will discuss our measurement of the hydrogen 2S-8D transition (a crucial transition for the proton radius puzzle), and our ongoing efforts to laser cool/slow hydrogen.

September 24, 2019 [P&A Colloquium] Dr. Chris Rasmussen CERN Using Trapped Antihydrogen to Probe Fundamental Symmetries

Antihydrogen - the antimatter equivalent the ordinary hydrogen atom - offers a unique way of probing fundamental symmetries. In particular, CPT symmetry (Charge, Parity and Time) requires that the spectrum of antihydrogen be identical to that of its ordinary matter cousin. In the ALPHA experiment at CERN, antihydrogen atoms are synthesized and magnetically trapped to enable spectroscopic measurements and subsequent comparison to the hydrogen spectrum. Of particular interest is the 1S-2S transition, which, due to its very narrow natural line width, allows for a particularly high precision test of CPT symmetry. Our best measurement of this transition frequency thus far has a relative error of just 2 parts in a trillion, making it one of the most precise measurements performed on an antimatter system. Antimatter gravity is another topic of growing interest, with several experiments aiming to make a first observation of the free-fall acceleration of antimatter. ALPHA-g is a new experiment which aims to measure this acceleration through the careful release of magnetically trapped antihydrogen atoms, eventually reaching a precision of around 1%. In this talk I will present the state-of-the art in antihydrogen physics and outline some of the measurements that will be possible in the near future.

September 25, 2019 (Wed, 4PM) Prof. Liang Liu Inst. of Optics and Fine Mechanics, CAS, Shanghai, China Laser cooling of atoms in an integrating sphere (Host: Hal Metcalf)

Typically, cold atoms are generated from an optical molasses (OM) or a magneto-optical trap (MOT). For an OM, three pairs of counter-propagating laser beams are used to cool atoms, while for a MOT, besides three pairs of lasers beams, a strong anti-Helmholtz magnetic field is applied to trap the cold atoms. However, both OM and MOT require complex configurations of laser beams, and also, large beam size to capture more cold atoms. In this talk, another scheme of laser cooling of atoms, called diffuse laser cooling, is introduced. The diffuse light is produced in an integrating sphere by multi-reflection of injected laser beams at the inner surface inside the sphere. The sphere, whose vacuum is kept around 10-6 Pa, is connected to a rubidium atom source to keep enough atoms in the background. With right detuning, the diffuse light can efficiently cool background atoms. This talk will present the results of diffuse light cooling in an integrating sphere. The results in a cylindrical cavity and in a tube will also be discussed. This talk will also include the application of diffuse light cooling to a compact cold atom clock.

October 7, 2019 Prof. Olivier Pfister University of Virginia Engineering large-scale quantum squeezing and entanglement in the quantum optical frequency comb (Host: Eden Figueroa)

The resonant (qu)modes of a single parametric oscillator (OPO) can be used to create single-, two-, and multitudinous-mode squeezed states, and some of the latter can be made into cluster states suitable for quantum computing. I will present several of these ideas, including the generation of hypercubic cluster states, and some experimental realizations in my group.

October 14, 2019 Prof. Michael Chini University of Central Florida Towards attosecond spectroscopy with industrial-grade lasers (Host: Tom Allison)

The field of attosecond science was first enabled by nonlinear compression of intense laser pulses to a duration below two optical cycles. Twenty years later, creating such short pulses still requires state-of-the-art few-cycle Ti:Sapphire laser amplifiers to most efficiently exploit “instantaneous” optical nonlinearities in noble gases for spectral broadening and parametric frequency conversion. In this talk, I will show that nonlinear compression can in fact be much more efficient when driven in molecular gases by long (~100-cycle) pulses from industrial-grade Yb-doped lasers. As the enhanced nonlinearity is linked to rotational motion, the dynamics of the process can be exploited for long-wavelength frequency conversion and to compress picosecond lasers.

November 20, 2019 [Wednesday, SCGP-102] Prof. Immanuel Bloch Max Planck Institute of Quantum Optics Quantum Matter under the Microscope (Host: Hal Metcalf)

More than 30 years ago, Richard Feynman outlined his vision of a quantum simulator for carrying out complex calculations on physical problems. Today, his dream is a reality in laboratories around the world. This has become possible by using complex experimental setups of thousands of optical elements, which allow atoms to be cooled to nanokelvin temperatures, where they almost come to rest. Recent experiments with quantum gas microscopes allow for an unprecedented view and control of such artificial quantum matter in new parameter regimes and with new probes. In our fermionic quantum gas microscope, we can detect both charge and spin degrees of freedom simultaneously, thereby gaining maximum information on the intricate interplay between the two in the paradigmatic Hubbard model. In my talk, I will show how we can reveal hidden magnetic order, directly image individual magnetic polarons or probe the fractionalisation of spin and charge in dynamical experiments. For the first time we thereby have access to directly probe non-local ‘hidden’ correlation properties of quantum matter and to explore its real space resolved dynamical features also far from equilibrium. Furthermore, I will show how quantum gas microscopy can open new avenues for the field of quantum chemistry when probing and controlling the formation of huge Rydberg macrodimers in optical lattices.

December 2, 2019 Thomas Mittiga UC Berkeley Quantum Sensing at High Pressures (Host: Hal Metcalf)

The nitrogen-vacancy center has emerged as a promising nanoscale quantum sensor for temperature, strain, electric and magnetic fields. By integrating NV centers directly into a diamond anvil cell (DAC) --- the workhorse of high pressure science --- we demonstrate in situ measurements of magnetism inside the pressure chamber, up to ~50 GPa and for temperatures ranging from 25-340K. In addition to operating the NV in a DC-sensing modality, we also use it to perform temperature dependent noise spectroscopy of Gadolinium, directly observing the Curie transition via changes in the Johnson noise. In contrast to conventional probes at high pressure, the NV-DAC allows for diffraction-limited spatial resolution within the high pressure chamber. Time permitting, I will move away from the NV center as a quantum sensor and introduce our recent work using a strongly coupled ensemble of NV and P1 centers (substitutional nitrogen defects) to explore emergent hydrodynamics.

December 6, 2019 (Dissertation Defense) Brian Arnold Velocity Dependence of the Adiabatic Rapid Passage Force (Host: Hal Metcalf)

From optical tweezers to Doppler molasses and magneto-optical traps, optical forces have been a powerful tool for advancing control of quantum systems. Recent experiments have explored optical forces relying on stimulated emission rather than spontaneous emission. The Adiabatic Rapid Passage (ARP) force uses alternating chirped light pulses to excite and stimulate atoms providing a coherent momentum exchange. To determine the usefulness of the ARP force, we measure its velocity dependence. The velocity dependence contains large peak and valley structures we did not expect to see. To better explore the structures, we measure the force as a function of Rabi frequency and chirp range for a particular set of velocities. The evolution of the force remains unclear and requires additional study, for which I have laid out a roadmap for future work.

December 18, 2019 Prof. Philip Bucksbaum Stanford  Imaging molecules with ultrafast x-rays, in space and time (Host: Tom Weinacht)

X-ray lasers promise to revolutionize the way we observe chemical dynamics in the laboratory.  I will discuss the current efforts and future opportunities to employ these sources for molecular movies.

2019