We consider the decoherence of a single localized electron spin due to its coupling lattice nuclear bath in semiconductor quantum computer architecture. In presence an external magnetic field and at low temperatures, dominant mechanism is spectral diffusion resonance frequency temporally fluctuating random associated with dipolar interaction induced flip-flops pairs. The dephasing this depends intricately on dynamics bath, making coupled problem difficult solve. provide formally exact...

We investigate pure dephasing decoherence (free induction decay and spin echo) of a qubit interacting with nuclear bath. While for infinite magnetic field $B$ the only mechanism is spectral diffusion due to dipolar flip-flops spins, decreasing hyperfine-mediated interactions between spins become important. give theory these which takes advantage their long-range nature. For thermal uncorrelated bath we show that our applicable down $B\ensuremath{\sim}10\text{ }\text{ }\mathrm{mT}$, allowing...

We investigate decoherence due to pure dephasing of a localized spin qubit interacting with nuclear bath. Although in the limit very large magnetic field only mechanism is spectral diffusion dipolar flip-flops spins, decreasing hyperfine-mediated interactions between spins become important. take advantage their long-range nature and resum leading terms an $1/N$ expansion time-evolution function ($N$, being number appreciably electron spin, large). For case thermal uncorrelated bath we show...

Silicon is promising for spin-based quantum computation because nuclear spins, a source of magnetic noise, may be eliminated through isotopic enrichment. Long spin decoherence times T2 have been measured in isotope-enriched silicon but come far short the T2=2T1 limit. The effect spins on well established. However, background electron from ever present residual phosphorus impurities can also produce significant decoherence. We study decay as function donor concentration, 29Si and temperature...

The silicon metal-oxide-semiconductor (MOS) material system is technologically important for the implementation of electron spin-based quantum information technologies. Researchers predict need an integrated platform in order to implement useful computation, and decades advancements microelectronics fabrication lends itself this challenge. However, fundamental concerns have been raised about MOS interface (e.g. trap noise, variations g-factor practical multi-QDs). Furthermore, two-axis...

A quantum cluster expansion method is developed for the problem of localized electron spin decoherence due to dipolar fluctuations lattice nuclear spins. At lowest order it provides a microscopic explanation Lorentzian diffusion Hahn echoes without resorting any phenomenological Markovian assumption. Our numerical results show remarkable agreement with recent echo experiments in phosphorus doped silicon.

We present a remarkable finding that recently discovered [G. S. Uhrig, Phys. Rev. Lett. 98, 100504 (2007)] series of pulse sequences, designed to optimally restore coherence qubit in the spin-boson model decoherence, is fact completely independent and generically valid for arbitrary dephasing Hamiltonians given sufficiently short delay times between pulses. The maximizes fidelity versus number applied pulses because series, with each additional pulse, cancels successive orders time expansion...

We describe how the spin coherence time of a localized electron in solids, i.e. solid state qubit, can be prolonged by applying designed resonance pulse sequences. In particular, echo decay due to spectral diffusion frequency induced non-Markovian temporal fluctuations nuclear flip-flop dynamics strongly suppressed using multiple-pulse sequences akin Carr-Purcell-Meiboom-Gill sequence magnetic resonance. Spin enhanced factors 4-10 GaAs quantum dot and Si:P computer architectures composite...

Donors in silicon hold considerable promise for emerging quantum technologies, due to their uniquely long electron spin coherence times. Bismuth donors differ from more widely studied group V donors, such as phosphorous, several significant respects: They have the strongest binding energy (70.98 meV), a large nuclear (I=9/2), and strong hyperfine coupling constant (A=1475.4 MHz). These larger scales allow us perform detailed test of theoretical models describing spectral diffusion mechanism...

Phosphorus-doped silicon single crystals with 0.19 % <= f 99.2 %, where is the concentration of 29^Si isotopes, are measured at 8 K using a pulsed electron spin resonance technique, thereby effect environmental nuclear spins on donor systematically studied. The linewidth as function shows good agreement theoretical analysis. We also report phase memory time T_M dependent both and crystal axis relative to external magnetic field.

The central spin decoherence problem has been researched for over 50 years in the context of both nuclear magnetic resonance and electron resonance. Until recently, theoretical models have employed phenomenological stochastic descriptions bath-induced noise. During last few years, cluster expansion methods provided a microscopic, quantum theory to study spectral diffusion spin. These proven be very accurate efficient problems nuclear-induced which hyperfine interactions with are much...

We have shown theoretically that efficient multiple-exciton generation (MEG) by a single photon can be observed in small nanocrystals. Our quantum simulations include hundreds of thousands exciton and multiexciton states demonstrate the complex time-dependent dynamics these closed electronic system yields saturated MEG effect on picosecond time scale. Including phonon relaxation confirms requires exciton-biexciton coupling to faster than time.

We present a cluster expansion method for approximating quantum spin-bath dynamics in terms of classical Gaussian stochastic process. The produces the two-point correlation function approximate bath, permitting rapid evaluation noise-mitigating control strategies without resorting to computationally intensive dynamical decoupling models. Our approximation is valid wide class models possessing negligible back-action and nearly-Gaussian noise. study several instances central spin decoherence...

Concatenated dynamical decoupling (CDD) pulse sequences hold much promise as a strategy to mitigate decoherence in quantum information processing. It is important investigate the actual performance of these strategies real systems that are promising qubit candidates. In this Rapid Communication, we compute echo decay concatenations Hahn sequence for solid-state electronic spin nuclear bath using cluster expansion technique. We find each level concatenation reverses effect successive levels...

We study Si:P donor electron spin decoherence due to anisotropic hyperfine (AHF) interaction with the surrounding nuclear bath. In particular, we clarify echo envelope modulation (ESEEM) in system and resonancelike contributions from spins various shells away P atoms. suggest an approach minimize AHF-induced by avoiding resonances orienting applied magnetic field along directions that can periodically eliminate dominant nearest neighbor Our remarkable agreement experiment demonstrates nearly...

We theoretically consider solid state nuclear spins in a semiconductor nanostructure environment as long-lived, high-fidelity quantum memory. In particular, we calculate, the limit of strong applied magnetic field, fidelity versus time P donor random bath environments Si and GaAs, lifetime excited intrinsic polarized GaAs environments. former situation, spin dephases due to spectral diffusion induced by dipolar interaction among nuclei bath. calculate decay memory context Hahn...

Decoherence of a localized electron spin in solid state material (the ``central spin'' problem) at low temperature is believed to be dominated by interactions with nuclear spins the lattice. This decoherence partially suppressed through application large magnetic field that splits energy levels and prevents depolarization. However, dephasing resulting from dynamical bath cannot removed this way. Fluctuations lead an uncertainty electron's precessional frequency process known as spectral...

Constructing high-fidelity control fields that are robust to control, system, and/or surrounding environment uncertainties is a crucial objective for quantum information processing. Using the two-state Landau-Zener model illustrative simulations of controlled qubit, we generate optimal controls $\ensuremath{\pi}/2$ and $\ensuremath{\pi}$ pulses investigate their inherent robustness uncertainty in magnitude drift Hamiltonian. Next, construct quantum-control protocol improve system-drift by...

We present pulsed electron-nuclear double resonance (ENDOR) experiments which enable us to characterize the coupling between bismuth donor spin qubits in Si and surrounding bath of 29Si impurities provides dominant decoherence mechanism (nuclear diffusion) at low temperatures (< 16 K). Decoupling from is predicted cluster correlation expansion simulations show near-complete suppression diffusion, optimal working points. The takes form sharply peaked divergences diffusion coherence time,...

We theoretically study the nuclear spin induced decoherence of a quantum dot in Si that is confined at SiGe interface. calculate time dependence on ${}^{73}$Ge barrier layer to evaluate importance Ge as well enrichment for long times. use atomistic tight-binding modeling an accurate account electron wave function which particularly important determining contact hyperfine interactions with spins. find times due spins natural concentrations be milliseconds. This suggests SiGe/Si devices...

We present a strategy for producing multiqubit gates that promise high fidelity with minimal tuning requirements. Our combines gap protection from the adiabatic theorem dynamical decoupling in complementary manner. Energy-level transition errors are protected by adiabaticity and remaining phase mitigated via decoupling. This is powerful way to divide conquer various error channels. In order accomplish this without violating no-go regarding black-box dynamically corrected [Phys. Rev. A 80,...