Abstract
Understanding and control of the spin relaxation time T1 is among the key challenges for spin-based qubits. A larger T1 is generally favored, setting the fundamental upper limit to the qubit coherence and spin readout fidelity. In GaAs quantum dots at low temperatures and high in-plane magnetic fields B, the spin relaxation relies on phonon emission and spin–orbit coupling. The characteristic dependence T1 ∝ B−5 and pronounced B-field anisotropy were already confirmed experimentally. However, it has also been predicted 15 years ago that at low enough fields, the spin–orbit interaction is replaced by the coupling to the nuclear spins, where the relaxation becomes isotropic, and the scaling changes to T1 ∝ B−3. Here, we establish these predictions experimentally, by measuring T1 over an unprecedented range of magnetic fields—made possible by lower temperature—and report a maximum T1 = 57 ± 15 s at the lowest fields, setting a record electron spin lifetime in a nanostructure.
Highlights
Understanding and control of the spin relaxation time T1 is among the key challenges for spinbased qubits
The decay of the energy stored in the qubit defines the relaxation time T1
The requirement for a sizable splitting, necessary for many of the protocols to initialize, measure, or manipulate spin qubits[5,6,7,8], imposes limitations on T1, which in turn might influence these protocols in a profound way[9,10,11]. This further motivates investigations of mechanisms and fundamental limits of the spin relaxation in quantum dots. To understand this process in a GaAs quantum dot spin qubit, one needs to consider that it involves the dissipation of both energy and angular momentum, i.e., spin
Summary
Understanding and control of the spin relaxation time T1 is among the key challenges for spinbased qubits. The energy splitting is due to the Zeeman term of an applied magnetic field B.
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