Signatures of Hyperfine, Spin-Orbit, and Decoherence Effects in a Pauli Spin Blockade

Abstract

We detect in real time inter-dot tunneling events in a weakly coupled two electron double quantum dot in GaAs. At finite magnetic fields, we observe two characteristic tunneling times, T d and T b , belonging to, respectively, a direct and a blocked (spin-flip-assisted) tunneling. The latter corresponds to lifting of a Pauli spin blockade and the tunneling times ratio η = T b /T d characterizes the blockade efficiency. We find pronounced changes in the behavior of η upon increasing the magnetic field, with η increasing, saturating and increasing again. We explain this behavior as due to the crossover of the dominant blockade lifting mechanism from the hyperfine to spin-orbit interactions and due to a change in the contribution of the charge decoherence.PACS numbers: 73.63. Kv, 73.23.Hk, 85.35.Gv, 76.60.Es Electron spins in semiconductor quantum dots are promising resources for quantum information processing [1,2]. Laterally gated dots [5] are especially attractive due to the flexibility and scalability [4] of their design, and the possibility to electrically initialize [5], manipulate [6,7], and measure [8, 9] the slowly relaxing [10,11] spin states. Pauli spin blockade (PSB) [12] plays a crucial role in electrical manipulations. PSB is established when the conservation of spin blocks a transition from an excited state, where two electrons in two dots have parallel spins, to the ground state, where they form a singlet in one dot. The spin can thus be detected by a local charge sensor as the presence or absence of a charge transition [13,14]. The blockade is lifted by spin flips, limiting the readout fidelities [15,16], as well as manipulations and preparations of quantum states. [17,18] In GaAs quantum dots, there are two important sources of electron spin flips: the spin-orbit coupling, and the hyperfine interaction with spins of atomic nuclei. Respectively, they dominate the spin relaxation time T 1 [19,20] and decoherence time T 2 [21-23]. Apart from causing detrimental effects, both of these can be utilized in quantum state manipulation as a means of coupling of the electrical control fields to spins [24][25][26][27]. It is known that the relative importance of these two effects changes with magnetic field strength and orientation [18,28,29]. By resolving the direct and spin-flip-assisted inter-dot tunneling, here we investigate experimentally the limit these factors impose on the effectiveness of PSB. We find a crossover in their dominance upon changing the magnetic field strength, which is fully consistent with our theory. Our results give guidance on how to increase the PSB effectiveness with importance for spin readout applications.Our device is a gate defined lateral double quantum dot (DQD), Fig. 1(a), weakly tunnel-coupled and isolated from reservoirs, with lead-dot tunneling rates of order Hz, and the inter-dot tunneling rate of order kHz. In this regime, where tunnel coupling energies are much smaller than orbital or charging energies, the two electron configurations span a basis of five states [...

Single hole spin relaxation probed by fast single-shot latched charge sensing

“…Also, our values of T 1 are about four orders of magnitude shorter than those in electronic GaAs dots at equivalent magnetic fields. Again, this is a consequence of much weaker SOI in the electronic systems 18,[57][58][59] and a strongly elongated shape of our dot 48 , which is known to enhance the spin-orbit coupling 21 . However, extrapolation of our values of T 1 to very low magnetic fields promises superior lifetime of the hole spin over that of the electron owing to the much weaker hyperfine interactions.…”

Consequences of Spin-Orbit Coupling at the Single Hole Level: Spin-Flip Tunneling and the Anisotropic g Factor

“…First, the HH in III-V materials experiences a strong spin-orbit interaction, causing the hole spin to rotate during tunneling [12,13,26]. In electronic devices this process was found to be orders of magnitude weaker [28]. One expects, therefore, that the Pauli blockade will be lifted for all (1,1)→(2,0) tunneling channels.…”

“…While g * = 0 is desired, in practice it should be small enough for the resulting Zeeman splitting to be smaller than the photon bandwidth [6,7]. Currently the longest spin coherence times have been demonstrated for electron spin qubits in 28 Si [9], but their coupling to light is challenging due to the indirect bandgap. GaAs electronic devices, while more promising [4,5], still require g-factor engineering.…”

Full counting statistics of spin-flip and spin-conserving charge transitions in Pauli-spin blockade

“…In this work, we choose the Pauli-spin blockade (PSB) effect in a DQD [32] to investigate the charge and spin dynamics because PSB is the simplest but most significant spin-correlated phenomenon that affects the electron dynamics in a DQD. Real-time charge sensing of a DQD holding two electrons in PSB has been reported in earlier studies, which showed that the charge transitions can be classified into spin-flip and spin-conserving transitions [33][34][35]. The spin-conserving transitions only occur when the two spins are antiparallel, while the spin-flip transitions change the spin configuration.…”