Single-Spin Relaxation in a Synthetic Spin-Orbit Field

Abstract

Strong magnetic field gradients can produce a synthetic spin-orbit interaction that allows for high fidelity electrical control of single electron spins. We investigate how a field gradient impacts the spin relaxation time T1 by measuring T1 as a function of magnetic field B in silicon. The interplay of charge noise, magnetic field gradients, phonons, and conduction band valleys leads to a maximum relaxation time of 160 ms at low field, a strong spin-valley relaxation hotspot at intermediate fields, and a B 4 scaling at high fields. T1 is found to decrease with lattice temperature T lat as well as with added electrical noise. In comparison, samples without micromagnets have a significantly longer T1. Optimization of the micromagnet design, combined with reductions in charge noise and electron temperature, may further extend T1 in devices with large magnetic field gradients.

Large, Tunable Valley Splitting and Single-Spin Relaxation Mechanisms in a Si / Six Ge1Hollmann1, Struck2, Langrock3 et al. 2020Phys. Rev. Applied988901View full textAdd to dashboardCite

“…The Si x Ge 1−x barrier layer separates charged defects at the gate dielectric oxide interface [14,16] from the qubits in the silicon quantum well (QW) and thus reduces qubit dephasing due to charge noise. The major challenge for scaling up in this material system is its difficult-to-control and reportedly small valley splitting E VS , mainly below 70 μeV [8,[17][18][19][20][21][22][23][24][25]. The excited valley * lars.schreiber@physik.rwth-aachen.de state may then be occupied either by thermal excitation [19,26] or by fast spin relaxation [27], severely hampering the qubit control.…”

Effect of Quantum Hall Edge Strips on Valley Splitting in Silicon Quantum Wells

“…However, spin qubits in silicon suffer from a twofold degeneracy of the conduction-band valleys [10][11][12], complicating quantum operation. While the valley splitting energy can be large in silicon metal-oxide-semiconductor devices [13], even allowing for qubit operation above one Kelvin [14,15], atomic-scale disorder in Si/SiGe heterostructures at the Si quantum well top interface yields a valley splitting energy that is typically modest and poorly controlled, with values ranging from 10 to 200 μeV in quantum dots [5,[16][17][18][19][20][21][22][23][24]. While Si/SiGe heterostructures may provide a superior host for scalable qubit arrays due to the low disorder, a key challenge is thus to increase the valley splitting energy for scalable quantum information.…”

Site-Selective Quantum Control in an Isotopically Enriched Si28/Si0.7Ge0.3 Quadruple Quantum Dot

“…Similar fluctuations in the coherence times have been observed in other devices [9][10][11] and may be due to sampling over a relatively small number of spin-carrying nuclei in the quantum well and SiGe barrier layers. Another reason for the fast dephasing in qubits 1 and 2 could be charge noise which has been shown to shorten T 1 [43] and T 2 [6] in the presence of field gradients and is discussed in the supplementary information [29]. Due to the wedge shaped geometry of the micromagnet, the field gradient experienced by qubits 1 and 2 is significantly larger than at sites 3 and 4 which is evident from the large change in field offsets B M i between dots 1-3, and a relatively small change in B M i between dots 3 and 4 (see Table 1).…”