scholarly journals Controllable freezing of the nuclear spin bath in a single-atom spin qubit

2020 ◽  
Vol 6 (27) ◽  
pp. eaba3442 ◽  
Author(s):  
Mateusz T. Mądzik ◽  
Thaddeus D. Ladd ◽  
Fay E. Hudson ◽  
Kohei M. Itoh ◽  
Alexander M. Jakob ◽  
...  
Keyword(s):  
Electron Spin ◽  
Nuclear Spin ◽  
Quantum Coherence ◽  
Spin Dynamics ◽  
Spin Fluctuations ◽  
Single Atom ◽  
Spin Qubits ◽  
Nuclear Dynamics ◽  
Spin Bath ◽  
Spin Qubit

The quantum coherence and gate fidelity of electron spin qubits in semiconductors are often limited by nuclear spin fluctuations. Enrichment of spin-zero isotopes in silicon markedly improves the dephasing time T2*, which, unexpectedly, can extend two orders of magnitude beyond theoretical expectations. Using a single-atom 31P qubit in enriched 28Si, we show that the abnormally long T2* is due to the freezing of the dynamics of the residual 29Si nuclei, caused by the electron-nuclear hyperfine interaction. Inserting a waiting period when the electron is controllably removed unfreezes the nuclear dynamics and restores the ergodic T2* value. Our conclusions are supported by a nearly parameter-free modeling of the 29Si nuclear spin dynamics, which reveals the degree of backaction provided by the electron spin. This study clarifies the limits of ergodic assumptions in nuclear bath dynamics and provides previously unidentified strategies for maximizing coherence and gate fidelity of spin qubits in semiconductors.

scholarly journals Semiclassical model for the dephasing of a two-electron spin qubit coupled to a coherently evolving nuclear spin bath

2011 ◽  
Vol 84 (3) ◽  
Author(s):  
Izhar Neder ◽  
Mark S. Rudner ◽  
Hendrik Bluhm ◽  
Sandra Foletti ◽  
Bertrand I. Halperin ◽  
...  
Keyword(s):  
Electron Spin ◽  
Nuclear Spin ◽  
Semiclassical Model ◽  
Spin Bath ◽  
Spin Qubit

Engineering Electronic Structure to Protect Phase Memory in Molecular Qubits by Minimising Orbital Angular Momentum

2018 ◽  
Author(s):  
Ana Maria Ariciu ◽  
David H. Woen ◽  
Daniel N. Huh ◽  
Lydia Nodaraki ◽  
Andreas Kostopoulos ◽  
...  
Keyword(s):  
Electron Spin ◽  
Quantum Coherence ◽  
Quantum Information Processing ◽  
Pulse Sequences ◽  
Grover Algorithm ◽  
Ligand Shell ◽  
Information Strategies ◽  
Spin Qubit ◽  
Molecular Spin ◽  
The Impact

Using electron spins within molecules for quantum information processing (QIP) was first proposed by Leuenberger and Loss (1), who showed how the Grover algorithm could be mapped onto a Mn12 cage (2). Since then several groups have examined two-level (S = ½) molecular spin systems as possible qubits (3-12). There has also been a report of the implementation of the Grover algorithm in a four-level molecular qudit (13). A major challenge is to protect the spin qubit from noise that causes loss of phase information; strategies to minimize the impact of noise on qubits can be categorized as corrective, reductive, or protective. Corrective approaches allow noise and correct for its impact on the qubit using advanced microwave pulse sequences (3). Reductive approaches reduce the noise by minimising the number of nearby nuclear spins (7-11), and increasing the rigidity of molecules to minimise the effect of vibrations (which can cause a fluctuating magnetic field via spin-orbit coupling) (9,11); this is essentially engineering the ligand shell surrounding the electron spin. A protective approach would seek to make the qubit less sensitive to noise: an example of the protective approach is the use of clock transitions to render spin states immune to magnetic fields at first order (12). Here we present a further protective method that would complement reductive and corrective approaches to enhancing quantum coherence in molecular qubits. The target is a molecular spin qubit with an effective 2S ground state: we achieve this with a family of divalent rare-earth molecules that have negligible magnetic anisotropy such that the isotropic nature of the electron spin renders the qubit markedly less sensitive to magnetic noise, allowing coherent spin manipulations even at room temperature. If combined with the other strategies, we believe this could lead to molecular qubits with substantial advantages over competing qubit proposals.<br>

scholarly journals Fundamental limits of electron and nuclear spin qubit lifetimes in an isolated self-assembled quantum dot

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
George Gillard ◽  
Ian M. Griffiths ◽  
Gautham Ragunathan ◽  
Ata Ulhaq ◽  
Callum McEwan ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Spin Relaxation ◽  
Nuclear Spin ◽  
Operating Conditions ◽  
External Control ◽  
Spin Qubits ◽  
Fundamental Limits ◽  
Trade Offs ◽  
Wide Range ◽  
Spin Qubit

AbstractCombining external control with long spin lifetime and coherence is a key challenge for solid state spin qubits. Tunnel coupling with electron Fermi reservoir provides robust charge state control in semiconductor quantum dots, but results in undesired relaxation of electron and nuclear spins through mechanisms that lack complete understanding. Here, we unravel the contributions of tunnelling-assisted and phonon-assisted spin relaxation mechanisms by systematically adjusting the tunnelling coupling in a wide range, including the limit of an isolated quantum dot. These experiments reveal fundamental limits and trade-offs of quantum dot spin dynamics: while reduced tunnelling can be used to achieve electron spin qubit lifetimes exceeding 1 s, the optical spin initialisation fidelity is reduced below 80%, limited by Auger recombination. Comprehensive understanding of electron-nuclear spin relaxation attained here provides a roadmap for design of the optimal operating conditions in quantum dot spin qubits.

scholarly journals Enhancing the Coherence of a Spin Qubit by Operating it as a Feedback Loop That Controls its Nuclear Spin Bath

2010 ◽  
Vol 105 (21) ◽  
Author(s):  
Hendrik Bluhm ◽  
Sandra Foletti ◽  
Diana Mahalu ◽  
Vladimir Umansky ◽  
Amir Yacoby
Keyword(s):  
Nuclear Spin ◽  
Feedback Loop ◽  
Spin Bath ◽  
Spin Qubit

scholarly journals Nuclear-spin-pattern control of electron-spin dynamics in a series of V(iv) complexes

2019 ◽  
Vol 10 (36) ◽  
pp. 8447-8454 ◽  
Author(s):  
Cassidy E. Jackson ◽  
Chun-Yi Lin ◽  
Spencer H. Johnson ◽  
Johan van Tol ◽  
Joseph M. Zadrozny
Keyword(s):  
Spin Relaxation ◽  
Electron Spin ◽  
Nuclear Spin ◽  
Spin Dynamics ◽  
Relaxation Times ◽  
Open Shell ◽  
Pattern Control ◽  
Electron Spin Dynamics

This report details how the design of specific nuclear-spin patterns on ligands modulates spin-relaxation times in a set of open-shell vanadium(iv) complexes.

scholarly journals Coherent control via weak measurements in P31 single-atom electron and nuclear spin qubits

2018 ◽  
Vol 98 (15) ◽  
Author(s):  
J. T. Muhonen ◽  
J. P. Dehollain ◽  
A. Laucht ◽  
S. Simmons ◽  
R. Kalra ◽  
...  
Keyword(s):  
Nuclear Spin ◽  
Coherent Control ◽  
Single Atom ◽  
Spin Qubits ◽  
Weak Measurements

scholarly journals Effect of electron-nuclear spin interactions for electron-spin qubits localized in InGaAs self-assembled quantum dots

2005 ◽  
Vol 97 (4) ◽  
pp. 043706 ◽  
Author(s):  
Seungwon Lee ◽  
Paul von Allmen ◽  
Fabiano Oyafuso ◽  
Gerhard Klimeck ◽  
K. Birgitta Whaley
Keyword(s):  
Quantum Dots ◽  
Electron Spin ◽  
Nuclear Spin ◽  
Spin Qubits ◽  
Spin Interactions ◽  
Self Assembled

Quantitative prediction of nuclear-spin-diffusion-limited coherence times of molecular quantum bits based on copper(ii)

2017 ◽  
Vol 53 (32) ◽  
pp. 4477-4480 ◽  
Author(s):  
S. Lenz ◽  
K. Bader ◽  
H. Bamberger ◽  
J. van Slageren
Keyword(s):  
Electron Spin ◽  
Nuclear Spin ◽  
Spin Diffusion ◽  
Spin Dynamics ◽  
Quantitative Prediction ◽  
Quantum Bits ◽  
Diffusion Limited ◽  
Frozen Solutions ◽  
Electron Spin Dynamics

We have investigated the electron spin dynamics in a series of copper(ii) β-diketonate complexes both in frozen solutions and doped solids. We simulate the coherence decay quantitatively without fit parameters.

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