@article { ISI:000552576600008,
title = {Fidelity of a sequence of SWAP operations on a spin chain},
journal = {Phys. Rev. B},
volume = {102},
number = {3},
year = {2020},
month = {JUL 27},
pages = {035439},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We consider the {\textquoteleft}{\textquoteleft}transport{{\textquoteright}{\textquoteright}} of the state of a spin across a Heisenberg-coupled spin chain via the use of repeated SWAP gates, starting with one of two states-one in which the leftmost spin is down and the others up, and one in which the leftmost two spins are in a singlet state (i.e., they are entangled), and the others are again all up. More specifically, we transport the state of the leftmost spin in the first case and the next-to-leftmost spin in the second to the other end of the chain, and then back again. We accomplish our SWAP operations here by increasing the exchange coupling between the two spins that we operate on from a base value J to a larger value J(SWAP) for a time t = pi(h) over bar /4J(SWAP). We determine the fidelity of this sequence of operations in a number of situations-one in which only nearest-neighbor coupling exists between spins and there is no magnetic dipole-dipole coupling or noise (the most ideal case), one in which we introduce next-nearest-neighbor coupling, but none of the other effects, and one in which all of these effects are present. In the last case, the noise is assumed to be quasistatic, i.e., the exchange couplings are each drawn from a Gaussian distribution, truncated to only nonnegative values. We plot the fidelity as a function of JSWAP to illustrate various effects, namely crosstalk due to coupling to other spins, as well as noise, that are detrimental to our ability to perform a SWAP operation. Our theory should be useful to the ongoing experimental efforts in building semiconductor-based spin quantum computer architectures.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.102.035439},
author = {Throckmorton, Robert E. and Das Sarma, S.}
}
@article {throckmorton_spontaneous_2020,
title = {Spontaneous symmetry breaking in a honeycomb lattice subject to a periodic potential},
journal = {Phys. Rev. Res.},
volume = {2},
number = {2},
year = {2020},
note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article},
month = {may},
abstract = {Motivated by recent developments in twisted bilayer graphene moire superlattices, we investigate the effects of electron-electron interactions in a honeycomb lattice with an applied periodic potential using a finite-temperature Wilson-Fisher momentum shell renormalization group (RG) approach. We start with a low-energy effective theory for such a system, at first giving a discussion of the most general case in which no point group symmetry is preserved by the applied potential, and then focusing on the special case in which the potential preserves a D-3 point group symmetry. As in similar studies of bilayer graphene, we find that, while the coupling constants describing the interactions diverge at or below a certain critical temperature T = T-c, it turns out that ratios of these constants remain finite and in fact provide information about what types of orders the system is becoming unstable to. However, in contrast to these previous studies, we only find isolated fixed rays, indicating that these orders are likely unstable to perturbations to the coupling constants. Our RG analysis leads to the qualitative conclusion that the emergent interaction-induced symmetry-breaking phases in this model system, and perhaps therefore by extension in twisted bilayer graphene, are generically unstable and fragile, and may thus manifest strong sample dependence.},
doi = {10.1103/PhysRevResearch.2.023225},
author = {Throckmorton, Robert E. and Das Sarma, S.}
}
@article {ISI:000456032500004,
title = {Conditions allowing error correction in driven qubits},
journal = {Phys. Rev. B},
volume = {99},
number = {4},
year = {2019},
month = {JAN 17},
pages = {045422},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We consider a qubit that is driven along its logical z axis, with noise along the z axis in the driving field Omega proportional to some function f (Omega), as well as noise along the logical x axis. We establish that whether or not errors due to both types of noise can be canceled out, even approximately, depends on the explicit functional form of f (Omega) by considering a power-law form, f (Omega) proportional to Omega(k). In particular, we show that such cancellation is impossible for k = 0, 1, or any even integer. However, any other odd integer value of k besides 1 does permit cancellation; in fact, we show that both types of errors can be corrected with a sequence of four square pulses of equal duration. We provide sets of parameters that correct for errors for various rotations and evaluate the error, measured by the infidelity, for the corrected rotations versus the naive rotations, i.e., the operations that, in the complete absence of noise, would produce the desired rotations (in this case a single pulse of appropriate duration and magnitude). We also consider a train of four trapezoidal pulses, which take into account the fact that there will be, in real experimental systems, a finite rise time, again providing parameters for error-corrected rotations that employ such pulse sequences. Our dynamical decoupling error correction scheme works for any qubit platform as long as the errors are quasistatic.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.99.045422},
author = {Throckmorton, Robert E. and S. Das Sarma}
}
@article {ISI:000478993000006,
title = {Simulation of the coupling strength of capacitively coupled singlet-triplet qubits},
journal = {Phys. Rev. B},
volume = {100},
number = {7},
year = {2019},
month = {AUG 6},
pages = {075411},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We consider a system of two purely capacitively coupled singlet-triplet qubits and numerically simulate the energy structure of four electrons in two double quantum dots with a large potential barrier between them. We calculate the interqubit coupling strength using an extended Hund-Mulliken approach which includes excited orbitals in addition to the lowest-energy orbital for each quantum dot. We show the coupling strength as a function of the qubit separation as well as plotting it against the detunings of the two double quantum dots and show that the general qualitative features of our results can be captured by a potential-independent toy model of the system.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.100.075411},
author = {Buterakos, Donovan and Throckmorton, Robert E. and S. Das Sarma}
}
@article { ISI:000423433700007,
title = {Crosstalk error correction through dynamical decoupling of single-qubit gates in capacitively coupled singlet-triplet semiconductor spin qubits},
journal = {PHYSICAL REVIEW B},
volume = {97},
number = {4},
year = {2018},
month = {JAN 29},
pages = {045431},
issn = {2469-9950},
doi = {10.1103/PhysRevB.97.045431},
author = {Buterakos, Donovan and Throckmorton, Robert E. and S. Das Sarma}
}
@article { ISI:000437110200003,
title = {Error correction for gate operations in systems of exchange-coupled singlet-triplet qubits in double quantum dots},
journal = {PHYSICAL REVIEW B},
volume = {98},
number = {3},
year = {2018},
month = {JUL 3},
pages = {035406},
issn = {2469-9950},
doi = {10.1103/PhysRevB.98.035406},
author = {Buterakos, Donovan and Throckmorton, Robert E. and S. Das Sarma}
}
@article { ISI:000446554000001,
title = {Failure of Kohn{\textquoteright}s theorem and the apparent failure of the f-sum rule in intrinsic Dirac-Weyl materials in the presence of a filled Fermi sea},
journal = {PHYSICAL REVIEW B},
volume = {98},
number = {15},
year = {2018},
month = {OCT 5},
pages = {155112},
issn = {2469-9950},
doi = {10.1103/PhysRevB.98.155112},
author = {Throckmorton, Robert E. and S. Das Sarma}
}
@article { ISI:000451606600001,
title = {Plasmon-pole approximation for many-body effects in extrinsic graphene},
journal = {PHYSICAL REVIEW B},
volume = {98},
number = {19},
year = {2018},
month = {NOV 28},
pages = {195140},
abstract = {We develop the plasmon-pole approximation (PPA) theory for calculating the carrier self-energy of extrinsic graphene as a function of doping density within analytical approximations to the GW random phase approximation (GW-RPA). Our calculated self-energy shows excellent quantitative agreement with the corresponding full GW-RPA calculation results in spite of the simplicity of the PPA, establishing the general validity of the plasmon-pole approximation scheme. We also provide a comparison between the PPA and the hydrodynamic approximation in graphene, and comment on the experimental implications of our findings.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.98.195140},
author = {Hwang, E. H. and Throckmorton, Robert E. and S. Das Sarma}
}
@article { ISI:000415568700001,
title = {Fast pulse sequences for dynamically corrected gates in singlet-triplet qubits},
journal = {PHYSICAL REVIEW B},
volume = {96},
number = {19},
year = {2017},
month = {NOV 17},
issn = {2469-9950},
doi = {10.1103/PhysRevB.96.195424},
author = {Throckmorton, Robert E. and Zhang, Chengxian and Yang, Xu-Chen and Wang, Xin and Barnes, Edwin and S. Das Sarma}
}
@article { ISI:000381485200004,
title = {Dynamics of two coupled semiconductor spin qubits in a noisy environment},
journal = {PHYSICAL REVIEW B},
volume = {94},
number = {4},
year = {2016},
month = {JUL 27},
issn = {2469-9950},
doi = {10.1103/PhysRevB.94.045435},
author = {S. Das Sarma and Throckmorton, Robert E. and Wu, Yang-Le}
}
@article { ISI:000370245900009,
title = {Noise-induced collective quantum state preservation in spin qubit arrays},
journal = {PHYSICAL REVIEW B},
volume = {93},
number = {8},
year = {2016},
month = {FEB 16},
issn = {2469-9950},
doi = {10.1103/PhysRevB.93.085420},
author = {Barnes, Edwin and Deng, Dong-Ling and Throckmorton, Robert E. and Wu, Yang-Le and S. Das Sarma}
}
@article { ISI:000360331300001,
title = {Many-body effects and ultraviolet renormalization in three-dimensional Dirac materials},
journal = {PHYSICAL REVIEW B},
volume = {92},
number = {11},
year = {2015},
month = {SEP 1},
issn = {1098-0121},
doi = {10.1103/PhysRevB.92.115101},
author = {Throckmorton, Robert E. and Hofmann, Johannes and Barnes, Edwin and S. Das Sarma}
}
@article { ISI:000345247900007,
title = {Quantum multicriticality in bilayer graphene with a tunable energy gap},
journal = {PHYSICAL REVIEW B},
volume = {90},
number = {20},
year = {2014},
month = {NOV 7},
issn = {1098-0121},
doi = {10.1103/PhysRevB.90.205407},
author = {Throckmorton, Robert E. and S. Das Sarma}
}