%0 Journal Article
%J Physical Review Letters
%D 2013
%T The Resonant Exchange Qubit
%A J. Medford
%A J. Beil
%A J. M. Taylor
%A E. I. Rashba
%A H. Lu
%A A. C. Gossard
%A C. M. Marcus
%X We introduce a solid-state qubit in which exchange interactions among confined electrons provide both the static longitudinal field and the oscillatory transverse field, allowing rapid and full qubit control via rf gate-voltage pulses. We demonstrate two-axis control at a detuning sweet-spot, where leakage due to hyperfine coupling is suppressed by the large exchange gap. A {\pi}/2-gate time of 2.5 ns and a coherence time of 19 {\mu}s, using multi-pulse echo, are also demonstrated. Model calculations that include effects of hyperfine noise are in excellent quantitative agreement with experiment.
%B Physical Review Letters
%V 111
%8 2013/7/31
%G eng
%U http://arxiv.org/abs/1304.3413v2
%N 5
%! Phys. Rev. Lett.
%R 10.1103/PhysRevLett.111.050501
%0 Journal Article
%J Nature Nanotechnology
%D 2013
%T Self-Consistent Measurement and State Tomography of an Exchange-Only Spin Qubit
%A J. Medford
%A J. Beil
%A J. M. Taylor
%A S. D. Bartlett
%A A. C. Doherty
%A E. I. Rashba
%A D. P. DiVincenzo
%A H. Lu
%A A. C. Gossard
%A C. M. Marcus
%X We report initialization, complete electrical control, and single-shot readout of an exchange-only spin qubit. Full control via the exchange interaction is fast, yielding a demonstrated 75 qubit rotations in under 2 ns. Measurement and state tomography are performed using a maximum-likelihood estimator method, allowing decoherence, leakage out of the qubit state space, and measurement fidelity to be quantified. The methods developed here are generally applicable to systems with state leakage, noisy measurements, and non-orthogonal control axes.
%B Nature Nanotechnology
%V 8
%P 654 - 659
%8 2013/9/1
%G eng
%U http://arxiv.org/abs/1302.1933v1
%N 9
%! Nature Nanotech
%R 10.1038/nnano.2013.168
%0 Journal Article
%J Physical Review Letters
%D 2011
%T Laser cooling and optical detection of excitations in a LC electrical circuit
%A J. M. Taylor
%A A. S. Sørensen
%A C. M. Marcus
%A E. S. Polzik
%X We explore a method for laser cooling and optical detection of excitations in a LC electrical circuit. Our approach uses a nanomechanical oscillator as a transducer between optical and electronic excitations. An experimentally feasible system with the oscillator capacitively coupled to the LC and at the same time interacting with light via an optomechanical force is shown to provide strong electro-mechanical coupling. Conditions for improved sensitivity and quantum limited readout of electrical signals with such an "optical loud speaker" are outlined.
%B Physical Review Letters
%V 107
%8 2011/12/27
%G eng
%U http://arxiv.org/abs/1108.2035v1
%N 27
%! Phys. Rev. Lett.
%R 10.1103/PhysRevLett.107.273601
%0 Journal Article
%J Physical Review Letters
%D 2010
%T Dynamic Nuclear Polarization in Double Quantum Dots
%A Michael Gullans
%A J. J. Krich
%A J. M. Taylor
%A H. Bluhm
%A B. I. Halperin
%A C. M. Marcus
%A M. Stopa
%A A. Yacoby
%A M. D. Lukin
%X We theoretically investigate the controlled dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. Three regimes of long-term dynamics are identified, including the build up of a large difference in the Overhauser fields across the dots, the saturation of the nuclear polarization process associated with formation of so-called "dark states," and the elimination of the difference field. We show that in the case of unequal dots, build up of difference fields generally accompanies the nuclear polarization process, whereas for nearly identical dots, build up of difference fields competes with polarization saturation in dark states. The elimination of the difference field does not, in general, correspond to a stable steady state of the polarization process.
%B Physical Review Letters
%V 104
%8 2010/6/4
%G eng
%U http://arxiv.org/abs/1003.4508v2
%N 22
%! Phys. Rev. Lett.
%R 10.1103/PhysRevLett.104.226807
%0 Journal Article
%J Physical Review B
%D 2007
%T Relaxation, dephasing, and quantum control of electron spins in double quantum dots
%A J. M. Taylor
%A J. R. Petta
%A A. C. Johnson
%A A. Yacoby
%A C. M. Marcus
%A M. D. Lukin
%X Recent experiments have demonstrated quantum manipulation of two-electron spin states in double quantum dots using electrically controlled exchange interactions. Here, we present a detailed theory for electron spin dynamics in two-electron double dot systems that was used to guide these experiments and analyze experimental results. The theory treats both charge and spin degrees of freedom on an equal basis. Specifically, we analyze the relaxation and dephasing mechanisms that are relevant to experiments and discuss practical approaches for quantum control of two-electron system. We show that both charge and spin dephasing play important roles in the dynamics of the two-spin system, but neither represents a fundamental limit for electrical control of spin degrees of freedom in semiconductor quantum bits.
%B Physical Review B
%V 76
%8 2007/7/13
%G eng
%U http://arxiv.org/abs/cond-mat/0602470v2
%N 3
%! Phys. Rev. B
%R 10.1103/PhysRevB.76.035315
%0 Journal Article
%J Physical Review Letters
%D 2005
%T Solid-state circuit for spin entanglement generation and purification
%A J. M. Taylor
%A W. Dür
%A P. Zoller
%A A. Yacoby
%A C. M. Marcus
%A M. D. Lukin
%X We show how realistic charge manipulation and measurement techniques, combined with the exchange interaction, allow for the robust generation and purification of four-particle spin entangled states in electrically controlled semiconductor quantum dots. The generated states are immunized to the dominant sources of noise via a dynamical decoherence-free subspace; all additional errors are corrected by a purification protocol. This approach may find application in quantum computation, communication, and metrology.
%B Physical Review Letters
%V 94
%8 2005/6/15
%G eng
%U http://arxiv.org/abs/cond-mat/0503255v2
%N 23
%! Phys. Rev. Lett.
%R 10.1103/PhysRevLett.94.236803
%0 Journal Article
%J Physical Review Letters
%D 2003
%T Long-lived memory for mesoscopic quantum bits
%A J. M. Taylor
%A C. M. Marcus
%A M. D. Lukin
%X We describe a technique to create long-lived quantum memory for quantum bits in mesoscopic systems. Specifically we show that electronic spin coherence can be reversibly mapped onto the collective state of the surrounding nuclei. The coherent transfer can be efficient and fast and it can be used, when combined with standard resonance techniques, to reversibly store coherent superpositions on the time scale of seconds. This method can also allow for ``engineering'' entangled states of nuclear ensembles and efficiently manipulating the stored states. We investigate the feasibility of this method through a detailed analysis of the coherence properties of the system.
%B Physical Review Letters
%V 90
%8 2003/5/20
%G eng
%U http://arxiv.org/abs/cond-mat/0301323v1
%N 20
%! Phys. Rev. Lett.
%R 10.1103/PhysRevLett.90.206803