[Paper Review] Non-reciprocal Pauli Spin Blockade in a Silicon Double Quantum Dot

Theodor Lundberg, David J. Ibberson+13 more|arXiv (Cornell University)|Oct 19, 2021

Quantum and electron transport phenomena54 references4 citations

TL;DR

This paper reports the first experimental observation of non-reciprocal Pauli spin blockade (PSB) in a silicon double quantum dot due to incoherent tunneling between spin manifolds. Using dispersive magnetospectroscopy across 16 charge configurations, the authors identify a 7.90 μeV coupling between electron spin states—the largest reported to date—indicating enhanced spin-orbit coupling and enabling all-electrical spin control via electric-dipole spin resonance.

ABSTRACT

Spin qubits in gate-defined silicon quantum dots are receiving increased attention thanks to their potential for large-scale quantum computing. Readout of such spin qubits is done most accurately and scalably via Pauli spin blockade (PSB), however various mechanisms may lift PSB and complicate readout. In this work, we present an experimental observation of a new, highly prevalent PSB-lifting mechanism in a silicon double quantum dot due to incoherent tunneling between different spin manifolds. Through dispersively-detected magnetospectroscopy of the double quantum dot in 16 charge configurations, we find the mechanism to be energy-level selective and non-reciprocal for neighbouring charge configurations. Additionally, using input-output theory we report a large coupling of different electron spin manifolds of 7.90 $μ$eV, the largest reported to date, indicating an enhanced spin-orbit coupling which may enable all-electrical qubit control.

Motivation & Objective

• To investigate the mechanisms lifting Pauli spin blockade (PSB) in silicon double quantum dots, which compromises high-fidelity spin qubit readout.
• To identify and characterize non-reciprocal, energy-level-selective PSB-lifting mechanisms in a CMOS-compatible silicon double quantum dot.
• To quantify the coupling between different electron spin manifolds using input-output theory and dispersive sensing.
• To assess the implications of enhanced spin-orbit coupling for all-electrical spin manipulation in silicon spin qubits.

Proposed method

• Dispersive magnetospectroscopy of a silicon double quantum dot using a superconducting LC resonator coupled to the device via gate G_T1.
• Measurement of relative phase shifts in the resonator response as a function of magnetic field across 16 charge configurations, identified as inter-charge transition (ICT) points.
• Application of input-output theory to model the parametric capacitance, decomposed into quantum and tunneling contributions, to simulate phase response.
• Use of the general expression for polarization and occupation probabilities to model the parametric capacitance response under slow and fast relaxation regimes.
• Simulation of magnetospectra using energy splittings, tunnel couplings, and thermal occupation probabilities, with parameters derived from experimental data and fitted to observed features.
• Incorporation of Landau-Zener transition effects at high magnetic fields to suppress phase shift signals beyond 0.2 T in simulations.

Experimental results

Research questions

• RQ1 What mechanisms cause non-reciprocal lifting of Pauli spin blockade in silicon double quantum dots?
• RQ2 How does incoherent tunneling between spin manifolds affect the dispersive detection of PSB in different charge configurations?
• RQ3 What is the magnitude of the coupling between different electron spin manifolds in this system?
• RQ4 Can enhanced spin-orbit coupling be inferred from the observed PSB-lifting behavior and resonator response?
• RQ5 What are the implications of a large spin-orbit coupling for all-electrical spin qubit control in silicon?

Key findings

• A new PSB-lifting mechanism was observed, driven by incoherent tunneling between spin manifolds, which is energy-level selective and non-reciprocal across neighboring charge configurations.
• The coupling between different electron spin manifolds was quantified at 7.90 μeV using input-output theory, the largest reported value to date.
• This large coupling indicates enhanced spin-orbit coupling, which could enable all-electrical spin manipulation via electric-dipole spin resonance (EDSR).
• The PSB-lifting mechanism is prevalent across 16 charge configurations, with non-reciprocal behavior observed in both (6,9)-(7,8) and (5,10)-(6,9) ICTs.
• Simulations using input-output theory with both quantum and tunneling capacitance contributions accurately reproduce the measured magnetospectra, confirming the role of fast relaxation in PSB lifting.
• The presence of Landau-Zener transitions at high magnetic fields (>0.2 T) suppresses the phase shift signal, consistent with experimental observations.