N. Tobias Jacobson
University of Southern California
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Featured researches published by N. Tobias Jacobson.
Physical Review B | 2015
John King Gamble; N. Tobias Jacobson; Erik Nielsen; Andrew David Baczewski; Jonathan E. Moussa; Ines Montano; Richard P. Muller
Last year, Salfi et al. made the first direct measurements of a donor wave function and found extremely good theoretical agreement with atomistic tight-binding [Salfi et al., Nat. Mater. 13, 605 (2014)]. Here, we show that multi-valley effective mass theory, applied properly, does achieve close agreement with tight-binding and hence gives reliable predictions. To demonstrate this, we variationally solve the coupled six-valley Shindo-Nara equations, including silicons full Bloch functions. Surprisingly, we find that including the full Bloch functions necessitates a tetrahedral, rather than spherical, donor central cell correction to accurately reproduce the experimental energy spectrum of a phosphorus impurity in silicon. We cross-validate this method against atomistic tight-binding calculations, showing that the two theories agree well for the calculation of donor-donor tunnel coupling. Further, we benchmark our results by performing a statistical uncertainty analysis, confirming that derived quantities such as the wave function profile and tunnel couplings are robust with respect to variational energy fluctuations. Finally, we apply this method to exhaustively enumerate the tunnel coupling for all donor-donor configurations within a large search volume, demonstrating conclusively that the tunnel coupling has no spatially stable regions. Though this instability is problematic for reliably coupling donor pairs for two-qubit operations, we identify specific target locations where donor qubits can be placed with scanning tunneling microscopy technology to achieve reliably large tunnel couplings.
Physical Review Letters | 2009
Silvano Garnerone; N. Tobias Jacobson; Stephan Haas; Paolo Zanardi
We study the random XY spin chain in a transverse field by analyzing the susceptibility of the ground state fidelity, numerically evaluated through a standard mapping of the model onto quasifree fermions. It is found that the fidelity susceptibility and its scaling properties provide useful information about the phase diagram. In particular it is possible to determine the Ising critical line and the Griffiths phase regions, in agreement with previous analytical and numerical results.
Physical Review B | 2009
N. Tobias Jacobson; Silvano Garnerone; Stephan Haas; Paolo Zanardi
The phase diagram of a quantum
Physical Review X | 2018
Patrick Harvey-Collard; Benjamin D’Anjou; Martin Rudolph; N. Tobias Jacobson; Jason Dominguez; Gregory A. Ten Eyck; Joel R. Wendt; Tammy Pluym; Michael Lilly; William A. Coish; Michel Pioro-Ladrière; Malcolm S. Carroll
XY
Physical Review A | 2008
Damian F. Abasto; N. Tobias Jacobson; Paolo Zanardi
spin chain with Gaussian-distributed random anisotropies and transverse fields is investigated, with focus on the fidelity susceptibility, a recently introduced quantum information theoretical measure. Monitoring the finite-size scaling of the probability distribution of this quantity as well as its average and typical values, we detect a disorder-induced disappearance of criticality and the emergence of Griffiths phases in this model. It is found that the fidelity susceptibility is not self-averaging near the disorder-free quantum-critical lines. At the Ising critical point the fidelity susceptibility scales as a disorder-strength independent stretched exponential of the system size, in contrast with the quadratic scaling at the corresponding point in the disorder-free
Physical Review A | 2011
N. Tobias Jacobson; Lorenzo Campos Venuti
XY
arXiv: Mesoscale and Nanoscale Physics | 2017
Ryan M. Jock; N. Tobias Jacobson; Patrick Harvey-Collard; Andrew Mounce; Vanita Srinivasa; D. R. Ward; John M. Anderson; Ron Manginell; Joel R. Wendt; Martin Rudolph; Tammy Pluym; John King Gamble; Andrew David Baczewski; Wayne Witzel; Malcolm S. Carroll
chain. Along the line where the average anisotropy vanishes the fidelity susceptibility appears to scale extensively, whereas in the disorder-free case this point is quantum critical with quadratic finite-size scaling.
arXiv: Mesoscale and Nanoscale Physics | 2018
Patrick Harvey-Collard; N. Tobias Jacobson; Chloe Bureau-Oxton; Ryan M. Jock; Vanita Srinivasa; Andrew Mounce; Daniel Ward; John M. Anderson; Ronald P. Manginell; Joel R. Wendt; Tammy Pluym; Michael Lilly; Dwight Luhman; Michel Pioro-Ladrière; Malcolm S. Carroll
The readout of semiconductor spin qubits based on spin blockade is fast but suffers from a small charge signal. Previous work suggested large benefits from additional charge mapping processes, however uncertainties remain about the underlying mechanisms and achievable fidelity. In this work, we study the single-shot fidelity and limiting mechanisms for two variations of an enhanced latching readout. We achieve average single-shot readout fidelities > 99.3% and > 99.86% for the conventional and enhanced readout respectively, the latter being the highest to date for spin blockade. The signal amplitude is enhanced to a full one-electron signal while preserving the readout speed. Furthermore, layout constraints are relaxed because the charge sensor signal is no longer dependent on being aligned with the conventional (2, 0) - (1, 1) charge dipole. Silicon donor-quantum-dot qubits are used for this study, for which the dipole insensitivity substantially relaxes donor placement requirements. One of the readout variations also benefits from a parametric lifetime enhancement by replacing the spin-relaxation process with a charge-metastable one. This provides opportunities to further increase the fidelity. The relaxation mechanisms in the different regimes are investigated. This work demonstrates a readout that is fast, has one-electron signal and results in higher fidelity. It further predicts that going beyond 99.9% fidelity in a few microseconds of measurement time is within reach.
Bulletin of the American Physical Society | 2018
N. Tobias Jacobson; Daniel Ward; Andrew David Baczewski; John King Gamble; Martin Rudolph; Malcolm S. Carroll
We explore the finite-temperature phase diagram of the anisotropic XY spin chain using the quantum Chernoff bound metric on thermal states. The analysis of the metric elements allows one to easily identify, in terms of different scaling with temperature, quasiclassical and quantum-critical regions. These results extend recent ones obtained using the Bures metric and show that different information-theoretic notions of distance can carry the same sophisticated information about the phase diagram of an interacting many-body system featuring quantum-critical points.
Bulletin of the American Physical Society | 2017
Andrew Mounce; Martin Rudolph; N. Tobias Jacobson; Patrick Harvey-Collard; Joel R. Wendt; Tammy Pluym; Jason Dominguez; Malcolm S. Carroll