Robust energy-selective tunneling readout of singlet-triplet qubits under large magnetic field gradient

Abstract

Fast and high-fidelity quantum state detection is essential for building robust spin-based quantum information processing platforms in semiconductors. The Pauli spin blockade (PSB)-based spin-to-charge conversion and its variants are widely used for the spin state discrimination of two-electron singlet-triplet (ST 0) qubits; however, the single-shot measurement fidelity is limited by either the low signal contrast, or the short lifetime of the triplet state at the PSB energy detuning, especially due to strong mixing with singlet states at large magnetic field gradients. Ultimately, the limited single-shot measurement fidelity leads to low visibility of quantum operations. Here, we demonstrate an alternative method to achieve spin-to-charge conversion of ST 0 qubit states using energy-selective tunneling between doubly occupied quantum dots (QDs) and electron reservoirs. We demonstrate a single-shot measurement fidelity of 90% and an S-T 0 oscillation visibility of 81% at a field gradient of 100 mT (~500 MHz h (g*•μ B) −1); this allows single-shot readout with full electron charge signal contrast and, at the same time, long and tunable measurement time with negligible effect of relaxation even at strong magnetic field gradients. Using an rf-sensor positioned opposite to the QD array, we apply this method to two ST 0 qubits and show high-visibility readout of two individual single-qubit gate operations is possible with a single rf single-electron transistor sensor. We expect our measurement scheme for two-electron spin states can be applied to various hosting materials and provides a simplified and complementary route for multiple qubit state detection with high accuracy in QD-based quantum computing platforms.

Single-Shot Readout of a Driven Hybrid Qubit in a GaAs Double Quantum Dot

“…Achieving a measurement fidelity ≈ 96.4%, readout visibility ≈ 92.6%, and quantum oscillation visibility ≈ 75%, the result facilitates efficient HQ state detection with fidelity in line with the stateof-the-art EST single-shot detections achieved in various semiconductor gate-defined QD qubits. 22,25 Figure 1a shows a scanning electron microscope image of a QD device similar to the one we measured. The device is designed to form up to four QDs used for qubits, but we focus on the right double QD by grounding the irrelevant gate electrodes.…”

Individual two-axis control of three singlet-triplet qubits in a micromagnet integrated quantum dot array

“…Overall, while the experiment shows successful initial demonstration for multiple qubit operation in QDs by straightforward extension of quantum measurement schemes developed in the past 5,35,38,43,53 , fuller control and measurement of qubits at least require larger number of high-frequency line setup and further optimization of magnet position or gate electrode to magnet clearance.…”

“…The device was placed on a plate in a dilution refrigerator at ~20 mK and in-plane magnetic field z,ext B of 500 mT was applied. The electron temperature, estimated with Coulomb blockade thermometry 33,34 , is approximately 230 mK 35 .…”

“…The spin-to-charge conversion is performed using Pauli spin blockade (PSB) with fast correlated double sampling (CDS) technique 35,38 . Figure 1c Figure 1d shows 1 T times at PSB readout detuning positions for Q1 to Q3.…”

“…Fast relaxation at I/M positions prevents performing high fidelity single-shot readout using conventional PSB readout especially in the large  z B regime. Recent works study various alternative schemes to overcome shortcomings of the PSB readout using electron latching 35,38,40,44 . We expect that latched readout can be straightforwardly used for Q1 and Q3 while reading out Q2 isolated from the reservoir from both sides needs modification of device design.…”