Remote Sensing and Control of Phase Qubits

We demonstrate a remote sensing design of phase qubits by separating the control and readout circuits from the qubit loop. This design improves measurement reliability because the control readout chip can be fabricated using more robust materials and can be reused to test different qubit chips. Typical qubit measurements such as Rabi oscillations, spectroscopy, and excited-state energy relaxation are presented.Comment: 3 pages, 4 figure

Diamond-nitrogen-vacancy electronic and nuclear spin-state anticrossings under weak transverse magnetic fields

We report on detailed studies of electronic and nuclear spin states in the diamond-nitrogen-vacancy (NV) center under weak transverse magnetic fields. We numerically predict and experimentally verify a previously unobserved NV hyperfine level anticrossing (LAC) occurring at bias fields of tens of gauss—two orders of magnitude lower than previously reported LACs at ∼ 500 and ∼ 1000 G axial magnetic fields. We then discuss how the NV ground-state Hamiltonian can be manipulated in this regime to tailor the NV's sensitivity to environmental factors and to map into the nuclear spin state.United States. Dept. of Defense. Assistant Secretary of Defense for Research & Engineering (Air Force Contract No. FA8721-05-C-0002)United States. Office of Naval Research (N00014-13-1-0316)United States. National Aeronautics and Space Administration ( Office of the Chief Technologist’s Space Technology Research Fellowship

High-sensitivity spin-based electrometry with an ensemble of nitrogen-vacancy centers in diamond

We demonstrate a spin-based, all-dielectric electrometer based on an ensemble of nitrogen-vacancy (NV[superscript −]) defects in diamond. An applied electric field causes energy-level shifts symmetrically away from the NV[superscript −]'s degenerate triplet states via the Stark effect; this symmetry provides immunity to temperature fluctuations allowing for shot-noise-limited detection. Using an ensemble of NV[superscript −]s, we demonstrate shot-noise-limited sensitivities approaching 1 (V/cm)/√Hz under ambient conditions, at low frequencies (<10 Hz), and over a large dynamic range (20 dB). A theoretical model for the ensemble of NV[superscript −]s fits well with measurements of the ground-state electric susceptibility parameter 〈k[subscript ⊥]〉. Implications of spin-based, dielectric sensors for micron-scale electric-field sensing are discussed.United States. National Aeronautics and Space Administration. Office of Chief Technologist (Space Technology Research Fellowship)United States. Air Force Office of Scientific Research. Presidential Early Career Award in Science and Engineerin

Sub-micrometer epitaxial Josephson junctions for quantum circuits

We present a fabrication scheme and testing results for epitaxial sub-micrometer Josephson junctions. The junctions are made using a high-temperature (1170 K) "via process" yielding junctions as small as 0.8 mu m in diameter by use of optical lithography. Sapphire (Al2O3) tunnel-barriers are grown on an epitaxial Re/Ti multilayer base-electrode. We have fabricated devices with both Re and Al top electrodes. While room-temperature (295 K) resistance versus area data are favorable for both types of top electrodes, the low-temperature (50 mK) data show that junctions with the Al top electrode have a much higher subgap resistance. The microwave loss properties of the junctions have been measured by use of superconducting Josephson junction qubits. The results show that high subgap resistance correlates to improved qubit performance

Low-light-level nonlinear optics with slow light

Electromagnetically induced transparency in an optically thick, cold medium creates a unique system where pulse-propagation velocities may be orders of magnitude less than $c$ and optical nonlinearities become exceedingly large. As a result, nonlinear processes may be efficient at low-light levels. Using an atomic system with three, independent channels, we demonstrate a quantum interference switch where a laser pulse with an energy density of $\sim23$ photons per $\lambda^2/(2\pi)$ causes a 1/e absorption of a second pulse.Comment: to be published in PR

Hamiltonian engineering with constrained optimization for quantum sensing and control

While quantum devices rely on interactions between constituent subsystems and with their environment to operate, native interactions alone often fail to deliver targeted performance. Coherent pulsed control provides the ability to tailor effective interactions, known as Hamiltonian engineering. We propose a Hamiltonian engineering method that maximizes desired interactions while mitigating deleterious ones by conducting a pulse sequence search using constrained optimization. The optimization formulation incorporates pulse sequence length and cardinality penalties consistent with linear or integer programming. We apply the general technique to magnetometry with solid state spin ensembles in which inhomogeneous interactions between sensing spins limit coherence. Defining figures of merit for broadband Ramsey magnetometry, we present novel pulse sequences which outperform known techniques for homonuclear spin decoupling in both spin-1/2 and spin-1 systems. When applied to nitrogen vacancy (NV) centers in diamond, this scheme partially preserves the Zeeman interaction while zeroing dipolar coupling between negatively charged NV - centers. Such a scheme is of interest for NV - magnetometers which have reached the NV - -NV - coupling limit. We discuss experimental implementation in NV ensembles, as well as applicability of the current approach to more general spin bath decoupling and superconducting qubit control.Air Force Contract (FA8702-15-D-0001