Fast Charge Sensing of Si/SiGe Quantum Dots via a High-Frequency Accumulation Gate

Abstract

Quantum dot arrays are a versatile platform for the implementation of spin qubits, as highbandwidth sensor dots can be integrated with single-, double-and triple-dot qubits yielding fast and high-fidelity qubit readout. However, for undoped silicon devices, reflectometry off sensor ohmics suffers from the finite resistivity of the two-dimensional electron gas (2DEG), and alternative readout methods are limited to measuring qubit capacitance, rather than qubit charge. By coupling a surface-mount resonant circuit to the plunger gate of a high-impedance sensor, we realized a fast charge sensing technique that is compatible with resistive 2DEGs. We demonstrate this by acquiring at high speed charge stability diagrams of double-and tripledot arrays in Si/SiGe heterostructures as well as pulsed-gate single-shot charge and spin readout with integration times as low as 2.4 µs.

Single-electron operations in a foundry-fabricated array of quantum dots

“…Figure 1b shows a schematic of the device with V i tuned to induce a few-electron double quantum dot underneath G 1 and G 4 . Source and drain contacts allow conventional I(V) transport characterization, while an inductor (wirebonded to G 4 ) allows gate-based reflectometry, in which the combination of a radio-frequency (RF) carrier (V RF ) and a homodyne detection circuit yields a demodulated voltage V H 19 . Bias tees connected to G 1−3 (not shown) allow the application of high-bandwidth voltage signals.…”

“…The reflectometry technique is similar to that described in ref. 19 , in which a sensor dot tunnel-coupled to two reservoirs was monitored via a SMD-based tank circuit wirebonded to the accumulation gate of the sensor. In this work, the sensor dot (located underneath G 4 ) is tunnel coupled only to one reservoir (source in Fig.…”

Sensitive radiofrequency readout of quantum dots using an ultra-low-noise SQUID amplifier

“…The resulting capacitance difference between the two qubit states can be monitored via a radio-frequency (RF) resonator bonded to one of the quantum dot electrodes. Similar dispersive shifts also occur at charge transitions in the quantum dots, such that the reflected signal assists with tuning to the desired electron occupation [14][15][16]. Dispersive readout has the advantage that it does not require a separate charge sensor, but often the capacitance sensitivity is insufficient for single-shot qubit readout even in systems with a long spin decay time [17][18][19][20][21][22][23].…”

Radio-Frequency Reflectometry in Silicon-Based Quantum Dots

“…However, in accumulation-mode devices, the large parasitic capacitance of the accumulation gates to the two-dimensional electron gas (2DEG) below provides a low-impedance leakage pathway to ground for the rf signal, complicating rf-reflectometry measurements. Previous works have addressed this problem by the use of circuit-board elements [20] and careful gate design [21,22].…”

“…For this approach, we mitigate the effects of the capacitance by optimizing the on-board elements and the device design. Second, we present the "split-gate style," where the rf signal is carried by a gate that is capacitively coupled to the 2DEG [20]. By an adaptation of the sample design, the leakage pathway to the Ohmic contact is blocked by a highly resistive channel.…”