Spin relaxation of a donor electron coupled to interface states

Abstract

An electron spin qubit in a silicon donor atom is a promising candidate for quantum information processing because of its long coherence time. To be sensed with a single-electron transistor, the donor atom is usually located near an interface, where the donor states can be coupled with interface states. Here we study the phonon-assisted spin-relaxation mechanisms when a donor is coupled to confined (quantum-dot-like) interface states. We find that both Zeeman interaction and spin-orbit interaction can hybridize spin and orbital states, each contributing to phonon-assisted spin relaxation in addition to the spin relaxation for a bulk donor or a quantum dot. When the applied magnetic field B is weak (compared to orbital spacing), the phonon assisted spin relaxation shows the B 5 dependence. We find that there are peaks (hot-spots) in the B-dependent and detuning dependent spin relaxation due to strong hybridization of orbital states with opposite spin. We also find spin relaxation dips (cool-spots) due to the interference of different relaxation channels. Qubit operations near spin relaxation hot-spots can be useful for the fast spin initialization and near cool-spots for the preservation of quantum information during the transfer of spin qubits.

Hyperfine-assisted decoherence of a phosphorus nuclear-spin qubit in silicon

“…We identify a promising parameter range where the electrical single-qubit operations are at least an order of magnitude faster than the decoherence, and the latter is dominated by dephasing due to 1/f charge noise. Our study complements earlier theory works where the decoherence of electron-spin and flip-flop qubits in the dot-donor system were described 14,23,24 .…”

“…We denote the eigenstates of H ch as |a and |b , as a reference to the anti-bonding (higher-energy) and the bonding (lower-energy) state. Note that a low-energy excited orbital, i.e., the valley pair of |i , is available at the interface 14,21,24 , with an excitation energy varying from a few tens to a few hundreds of microelectronvolts. We disregard this state in our minimal model, assuming that its excitation energy is much larger than the tunnel coupling.…”

Fast spin-valley-based quantum gates in Si with micromagnets

“…Effective electric dipole of a spin qubit An important feature of a Si QD is the presence of a low-lying valley excited state, which affects a spin qubit [31][32][33][34][35][36][37][38][39][40][41][42][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63] . In the presence of the s-SOC, the spin and the valley states would mix, making it possible for electrically induced spin-flip transitions [20][21][22] .…”

“…However, further improvement to the fidelity of quantum gates for spin qubits in Si QDs could be hindered by the complex environment, particularly the valley degree of freedom in the conduction band and new decoherence channels due to charge noise that are opened by the introduction of micromagnets. For example, the valley states lead to a spinvalley hot spot (SVH) of spin relaxation [31][32][33][34][35][36][37][38][39][40] , which could be a detrimental effect. Charge noise-induced dephasing and relaxation have also been observed experimentally, though clear theoretical understanding remains lacking 38,39,41 .…”

“…Charge noise-induced dephasing and relaxation have also been observed experimentally, though clear theoretical understanding remains lacking 38,39,41 . The interplay between s-SOC and valley states remains to be explored 31,33,36,37,40,42 .…”