Bulletin of the American Physical Society
39th Annual Meeting of the APS Division of Atomic, Molecular, and Optical Physics
Volume 53, Number 7
Tuesday–Saturday, May 27–31, 2008; State College, Pennsylvania
Session P2: Controlling Electron and Nuclear Spins |
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Chair: Lilian Childress, Bates College Room: Kern Building 112 |
Friday, May 30, 2008 11:00AM - 11:36AM |
P2.00001: Manipulating single electron spins and coherence in quantum dots Invited Speaker: The non-destructive detection of a single electron spin in a quantum dot (QD) is demonstrated using a time- averaged magneto-optical Kerr rotation measurement\footnote{J. Berezovsky, M. H. Mikkelsen, O. Gywat, N. G. Stoltz, L. A. Coldren, and D. D. Awschalom, Science 314, 1916 (2006).}. This technique provides a means to directly probe the spin off- resonance, thus minimally disturbing the system. Furthermore, the ability to sequentially initialize, manipulate, and read out the state of a qubit, such as an electron spin in a quantum dot, is necessary for virtually any scheme for quantum information processing. In addition to the time-averaged measurements, we have extended the single dot KR technique into the time domain with pulsed pump and probe lasers, allowing the observation of the coherent evolution of an electron spin state\footnote{M. H. Mikkelsen, J. Berezovsky, N. G. Stoltz, L. A. Coldren, and D. D. Awschalom, Nature Physics 3, 770 (2007).}. The dot is formed by interface fluctuations of a GaAs quantum well and embedded in a diode structure to allow controllable gating/charging of the QD. To enhance the small single spin signal, the QD is positioned within a vertical optical cavity. Observations of coherent single spin precession in an applied magnetic field allow a direct measurement of the electron g-factor and transverse spin lifetime. These measurements reveal information about the relevant spin decoherence mechanisms, while also providing a sensitive probe of the local nuclear spin environment. Finally, we have recently eveloped a scheme for high speed all-optical manipulation of the spin state that enables multiple operations within the coherence time\footnote{J. Berezovsky, M. H. Mikkelsen, N. G. Stoltz, L. A. Coldren, and D. D. Awschalom, accepted for publication (2008).}. The results represent progress toward the control and coupling of single spins and photons for quantum information processing\footnote{S. Ghosh, W.H. Wang, F. M. Mendoza, R. C. Myers, X. Li, N. Samarth, A. C. Gossard, and D. D. Awschalom, Nature Materials, 5, 267 (2006).} as well as quantum non-demolition measurements of a single spin. [Preview Abstract] |
Friday, May 30, 2008 11:36AM - 12:12PM |
P2.00002: Coupled Electronic and Nuclear Spin Quantum Registers in Diamond Invited Speaker: Building scalable quantum information systems is a central challenge facing modern science. One promising approach is based on quantum registers composed of several quantum bits that are coupled together via optical channels. We discuss experiments that demonstrate addressing, preparation, and coherent control of individual nuclear spin qubits in the diamond lattice at room temperature. We have measured spin coherence times exceeding milliseconds, and observed coherent coupling to nearby electronic and nuclear spins. Robust initialization of a two-qubit register and transfer of arbitrary quantum states between electron and nuclear spin qubits has been achieved. Our results show that coherent operations are possible with individual solid-state qubits whose coherence properties approach those for isolated atoms and ions. The resulting electron-nuclear few-qubit registers can potentially serve as small processor nodes in a quantum network where the electron spins are coupled by optical photons to generate entanglement, and the nuclear spins serve as a resource for quantum memory and quantum logic operations. [Preview Abstract] |
Friday, May 30, 2008 12:12PM - 12:48PM |
P2.00003: High-sensitivity diamond magnetometer with nanoscale resolution Invited Speaker: The detection of weak magnetic fields with high spatial resolution is an important problem in diverse areas ranging from fundamental physics and material science to data storage and biomedical science. Here we describe a novel approach to magnetometry that takes advantage of recently developed techniques for coherent control of solid-state electronic spin quantum bits. To be specific, we investigate the use of spins associated with Nitrogen-Vacancy (NV) centers in diamond. Two key features distinguish our approach: the possibility to confine the sensing spins into a solid sample of nanometer dimensions that can be brought into direct proximity of a localized magnetic field source; and the potential of achieving high spin densities while maintaining good coherence properties, enabling the detection of sub-femtotesla magnetic fields. The resulting magnetic sensor, which can operate at room-temperature, ambient conditions, is projected to provide an unprecedented combination of ultra-high sensitivity and spatial resolution. As an example, we show that this could enable sensing of nanotesla magnetic fields with resolution well below 50 nanometers --allowing for the detection of a single nuclear spin's precession within one second. Finally, we describe first experiments toward the realization of these ideas. [Preview Abstract] |
Friday, May 30, 2008 12:48PM - 1:24PM |
P2.00004: Controlling electron and nuclear spins in double quantum dots Invited Speaker: Hyperfine interactions limit electron spin coherence times in GaAs quantum dots. By separating a spin singlet state on a chip, we measure an ensemble averaged spin dephasing time T$_{2}^{\ast }$ of 10 ns, limited by the contact hyperfine interaction with the GaAs host nuclei [1]. We use electrical control of the exchange interaction to drive coherent spin rotations. Exchange driven spin rotations are used to implement a ``singlet-triplet spin echo'' pulse sequence, which leads to a spin coherence time, T$_{2}$, exceeding 1 microsecond. We show that nuclear spins can be polarized by controlling two-electron spin states near the anti-crossing of the singlet (S) and triplet (T$_{+})$. An initialized S state is cyclically brought into resonance with the T$_{+}$ state, where hyperfine fields drive rapid rotations between S and T$_{+}$, `flipping' an electron spin and `flopping' a nuclear spin [2]. The resulting Overhauser field approaches 80 mT, in agreement with a simple rate-equation model. A self-limiting pulse sequence is developed that allows the steady-state nuclear polarization to be set using a gate voltage. \newline [1] J. R. Petta et al., Science \textbf{309}, 2180 (2005). \newline [2] J. R. Petta, J. M. Taylor \textit{et al.}, Phys. Rev. Lett. (in press). [Preview Abstract] |
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