Will Shanks

Bio: Will Shanks is an academic researcher from IBM. The author has contributed to research in topics: Persistent current & Cantilever. The author has an hindex of 12, co-authored 20 publications receiving 867 citations. Previous affiliations of Will Shanks include Yale University & Princeton University.

Persistent Currents in Normal Metal Rings

Abstract: Quantum mechanics predicts that the equilibrium state of a resistive metal ring will contain a dissipationless current. This persistent current has been the focus of considerable theoretical and experimental work, but its basic properties remain a topic of controversy. The main experimental challenges in studying persistent currents have been the small signals they produce and their exceptional sensitivity to their environment. We have developed a technique for detecting persistent currents that allows us to measure the persistent current in metal rings over a wide range of temperatures, ring sizes, and magnetic fields. Measurements of both a single ring and arrays of rings agree well with calculations based on a model of non-interacting electrons.

High quality mechanical and optical properties of commercial silicon nitride membranes

Abstract: We have measured the optical and mechanical loss of commercial silicon nitride membranes. We find that 50nm thick, 1mm2 membranes have mechanical Q>106 at 293K, and Q>107 at 300mK, well above what has been observed in devices with comparable dimensions. The near-IR optical loss at 293K is less than 2×10−4. This combination of properties make these membranes attractive candidates for studying quantum effects in optomechanical systems.

Low-Disorder Microwave Cavity Lattices for Quantum Simulation with Photons

Abstract: We assess experimentally the suitability of coupled-transmission-line resonators for studies of quantum phase transitions of light. We have measured devices with low photon hopping rates $t/2\ensuremath{\pi}=0.8$ MHz to quantify disorder in individual cavity frequencies. The observed disorder is consistent with small imperfections in fabrication. We studied the dependence of the disorder on transmission-line geometry and used our results to fabricate devices with disorder less than two parts in ${10}^{4}$. The normal-mode spectrum of devices with a high photon hopping rate $t/2\ensuremath{\pi}=31$ MHz shows little effect of disorder, rendering resonator arrays a good backbone for the study of condensed-matter physics with photons.

Investigating surface loss effects in superconducting transmon qubits

Abstract: Superconducting qubits are sensitive to a variety of loss mechanisms including dielectric loss from interfaces. By changing the physical footprint of the qubit, it is possible to modulate sensitivity to surface loss. Here, we show a systematic study of planar superconducting transmons of differing physical footprints to optimize the qubit design for maximum coherence. We find that qubits with small footprints are limited by surface loss and that qubits with large footprints are limited by other loss mechanisms, which are currently not understood.

Measurement of the full distribution of persistent current in normal-metal rings.

Abstract: We have measured the persistent current in individual normal metal rings over a wide range of magnetic fields. From this data, we extract the first six cumulants of the single-ring persistent current distribution. Our results are consistent with the prediction that this distribution should be nearly Gaussian for diffusive metallic rings. This measurement highlights the sensitivity of persistent current to the mesoscopic fluctuations within a single isolated coherent volume.

Strong dispersive coupling of a high-finesse cavity to a micromechanical membrane.

Abstract: In recent years micromechanical devices have been developed that can strongly couple to light, by integrating them within optical cavities. A main goal has been to cool the devices optomechanically, freezing out all thermal vibrations, so that the object's motion eventually becomes limited by quantum mechanical fluctuations. This would make it possible to study a new range of quantum behaviour of mechanical objects. Thompson et al. report an improved design of such a system, involving a movable membrane sandwiched between two rigid high-quality mirrors. In previous designs one of the mirrors had to double-up as a microresonator. The new device achieves substantial cooling, from room temperature to 6.8 mK. It should eventually be possible to reach the quantum-limited ground state with this system. A report on an improved design of an optomechanical system in which a movable membrane is placed between two rigid high-quality mirrors, as opposed to previous designs where one of the mirrors has a double function as the microresonator; it's claimed that it is feasible to reach the quantum-limited ground state with this new design. Macroscopic mechanical objects and electromagnetic degrees of freedom can couple to each other through radiation pressure. Optomechanical systems in which this coupling is sufficiently strong are predicted to show quantum effects and are a topic of considerable interest. Devices in this regime would offer new types of control over the quantum state of both light and matter1,2,3,4, and would provide a new arena in which to explore the boundary between quantum and classical physics5,6,7. Experiments so far have achieved sufficient optomechanical coupling to laser-cool mechanical devices8,9,10,11,12, but have not yet reached the quantum regime. The outstanding technical challenge in this field is integrating sensitive micromechanical elements (which must be small, light and flexible) into high-finesse cavities (which are typically rigid and massive) without compromising the mechanical or optical properties of either. A second, and more fundamental, challenge is to read out the mechanical element’s energy eigenstate. Displacement measurements (no matter how sensitive) cannot determine an oscillator’s energy eigenstate13, and measurements coupling to quantities other than displacement14,15,16 have been difficult to realize in practice. Here we present an optomechanical system that has the potential to resolve both of these challenges. We demonstrate a cavity which is detuned by the motion of a 50-nm-thick dielectric membrane placed between two macroscopic, rigid, high-finesse mirrors. This approach segregates optical and mechanical functionality to physically distinct structures and avoids compromising either. It also allows for direct measurement of the square of the membrane’s displacement, and thus in principle the membrane’s energy eigenstate. We estimate that it should be practical to use this scheme to observe quantum jumps of a mechanical system, an important goal in the field of quantum measurement.

Realizing effective magnetic field for photons by controlling the phase of dynamic modulation

Abstract: By considering a resonator lattice in which the coupling constants between the resonators are harmonically modulated in time and by controlling the spatial distribution of the modulation phases, scientists introduce a scheme that can generate an effective magnetic field for photons, without the use of magneto-optical effects.

Microwave photonics with superconducting quantum circuits

Abstract: In the past 20 years, impressive progress has been made both experimentally and theoretically in superconducting quantum circuits, which provide a platform for manipulating microwave photons. This emerging field of superconducting quantum microwave circuits has been driven by many new interesting phenomena in microwave photonics and quantum information processing. For instance, the interaction between superconducting quantum circuits and single microwave photons can reach the regimes of strong, ultra-strong, and even deep-strong coupling. Many higher-order effects, unusual and less familiar in traditional cavity quantum electrodynamics with natural atoms, have been experimentally observed, e.g., giant Kerr effects, multi-photon processes, and single-atom induced bistability of microwave photons. These developments may lead to improved understanding of the counterintuitive properties of quantum mechanics, and speed up applications ranging from microwave photonics to superconducting quantum information processing. In this article, we review experimental and theoretical progress in microwave photonics with superconducting quantum circuits. We hope that this global review can provide a useful roadmap for this rapidly developing field.

Bidirectional and efficient conversion between microwave and optical light

Abstract: An optomechanical system that converts microwaves to optical frequency light and vice versa is demonstrated. The technique achieves a conversion efficiency of approximately 10%. The results indicate that the device could work at the quantum level, up- and down-converting individual photons, if it were cooled to millikelvin temperatures. It could, therefore, form an integral part of quantum-processor networks.