Person:

Kolkowitz, S

We study theoretically the measurement of a mechanical oscillator using a single two-level system as a detector. In a recent experiment, we used a single electronic spin associated with a nitrogen–vacancy center in diamond to probe the thermal motion of a magnetized cantilever at room temperature (Kolkowitz et al 2012 Science 335 1603). Here, we present a detailed analysis of the sensitivity limits of this technique, as well as the possibility to measure the zero-point motion of the oscillator. Further, we discuss the issue of measurement backaction in sequential measurements and find that although backaction heating can occur, it does not prohibit the detection of zero-point motion. Throughout the paper, we focus on the experimental implementation of a nitrogen–vacancy center coupled to a magnetic cantilever; however, our results are applicable to a wide class of spin–oscillator systems. The implications for the preparation of nonclassical states of a mechanical oscillator are also discussed.

Mechanical systems can be influenced by a wide variety of small forces, ranging from gravitational to optical, electrical, and magnetic. When mechanical resonators are scaled down to nanometer-scale dimensions, these forces can be harnessed to enable coupling to individual quantum systems. We demonstrate that the coherent evolution of a single electronic spin associated with a nitrogen vacancy center in diamond can be coupled to the motion of a magnetized mechanical resonator. Coherent manipulation of the spin is used to sense driven and Brownian motion of the resonator under ambient conditions with a precision below 6 picometers. With future improvements, this technique could be used to detect mechanical zero-point fluctuations, realize strong spin-phonon coupling at a single quantum level, and implement quantum spin transducers.

We experimentally demonstrate the use of a single electronic spin to measure the quantum dynamics of distant individual nuclear spins from within a surrounding spin bath. Our technique exploits coherent control of the electron spin, allowing us to isolate and monitor nuclear spins weakly coupled to the electron spin. Specifically, we detect the evolution of distant individual C13 nuclear spins coupled to single nitrogen vacancy centers in a diamond lattice with hyperfine couplings down to a factor of 8 below the electronic spin bare dephasing rate. Potential applications to nanoscale magnetic resonance imaging and quantum information processing are discussed.

Nitrogen-vacancy (NV) centers in diamond have recently emerged as a promising new system for quantum information and nanoscale sensing applications. They have long coherence times at room temperature and can be positioned in proximity to the diamond surface, enabling magnetometry with high spatial resolution and coherent coupling to other quantum systems. This thesis presents three experiments in which single NV centers were used to sense magnetic fields at the nanometer scale. In the first experiment, the coherent evolution of a single NV spin is coupled to the motion of a magnetized mechanical resonator tens of nanometers from the NV. Coherent manipulation of the spin is used to sense the driven and Brownian motion of the resonator under ambient conditions, with picometer-scale sensitivity to motion. Future applications of this technique include the detection of the zero-point fluctuations of a mechanical resonator, the realization of strong spin-phonon coupling at a single quantum level, and the implementation of quantum spin transducers. In the second experiment, a single NV electronic spin is used to measure the quantum dynamics of distant individual nuclear spins from within a surrounding spin bath. The demonstrated sensing technique dramatically increases the potential size of NV based quantum registers for quantum information applications, and provides a new method for nanoscale magnetic resonance imaging of single nuclear spins. In the third experiment, single NV electronic spins are used to probe magnetic Johnson noise in the vicinity of conductive silver films. Measurements of polycrystalline silver films over a range of distances (20-200 nanometers) and temperatures (10-300 Kelvin) are consistent with the classically expected behavior of the magnetic fluctuations. However, Johnson noise is found to be dramatically suppressed next to single-crystal films, indicative of a substantial deviation from Ohm's law arising from the ballistic motion of the electrons in the metal. These result demonstrate that our technique provides a general, non-invasive probe of local electron transport in samples of arbitrary size and dimensionality, which can be used to explore materials response to localized impurities and the interplay between transport, interactions and disorder at the nanoscale.

Isolated electronic and nuclear spins in solids are at present being actively explored for potential quantum-computing applications. Spin degrees of freedom provide an excellent quantum memory, owing to their weak magnetic interactions with the environment. For the same reason, however, it is difficult to achieve controlled interactions of spins over distances larger than tens of nanometres. Here we propose a new realization of a quantum data bus for spin qubits where spins are coupled to the motion of magnetized mechanical resonators through magnetic-field gradients. Provided that the mechanical system is charged, the magnetic moments associated with spin qubits can be effectively amplified to enable a coherent spin–spin coupling over long distances through Coulomb forces. Our approach is applicable to a wide class of electronic spin qubits, which can be localized near magnetized tips and can be used for the implementation of hybrid quantum-computing architectures.

We propose a space-based gravitational wave (GW) detector consisting of two spatially separated, drag-free satellites sharing ultrastable optical laser light over a single baseline. Each satellite contains an optical lattice atomic clock, which serves as a sensitive, narrowband detector of the local frequency of the shared laser light. A synchronized two-clock comparison between the satellites will be sensitive to the effective Doppler shifts induced by incident GWs at a level competitive with other proposed space-based GW detectors, while providing complementary features. The detected signal is a differential frequency shift of the shared laser light due to the relative velocity of the satellites, and the detection window can be tuned through the control sequence applied to the atoms’ internal states. This scheme enables the detection of GWs from continuous, spectrally narrow sources, such as compact binary inspirals, with frequencies ranging from