Coherent transfer of quantum information in a silicon double quantum dot using resonant SWAP gates

Abstract

Solid state quantum processors based on spins in silicon quantum dots are emerging as a powerful platform for quantum information processing [1][2][3]. High fidelity single-and two-qubit gates have recently been demonstrated [2][3][4][5][6] and large extendable qubit arrays are now routinely fabricated [7,8]. However, two-qubit gates are mediated through nearest-neighbor exchange interactions [1,9], which require direct wavefunction overlap. This limits the overall connectivity of these devices and is a major hurdle to realizing error correction [10], quantum random access memory [11], and multi-qubit quantum algorithms [12]. To extend the connectivity, qubits can be shuttled around a device using quantum SWAP gates, but phase coherent SWAPs have not yet been realized in silicon devices [2][3][4][5][6]. Here, we demonstrate a new single-step resonant SWAP gate. We first use the gate to efficiently initialize and readout our double quantum dot. We then show that the gate can move spin eigenstates in 100 ns with average fidelityF (p) SWAP = 98 %. Finally, the transfer of arbitrary two-qubit product states is benchmarked using state tomography and Clifford randomized benchmarking [5,13], yielding an average fidelity ofF (c) SWAP = 84 % for gate operation times of ∼300 ns. Through coherent spin transport, our resonant SWAP gate enables the coupling of non-adjacent qubits, thus paving the way to large scale experiments using silicon spin qubits.In this work, we use two sites of a quadruple quantum dot fabricated on a 28 Si/SiGe heterostructure [inset of Fig. 1(a)] [8]. Electric dipole spin resonance (EDSR) [14,15] enables single-spin control and an on-chip micromagnet detunes the frequency of each spin to enable site-selective control [8,16]. For demonstration purposes, we use two dots in the device with qubits accumulated under plunger gates P 3 and P 4 . We hereafter refer to the two qubits as Q 3 and Q 4 , respectively. The charge stability diagram of this DQD is shown in Fig. 1(a) and quantum control is performed in the (N i , N i+1 ) = (1, 1) charge configuration, where N i denotes the number of electrons on dot i. We measure the state of Q 4 through spin-selective tunneling to a drain reservoir accumulated beneath gate D 3 [17].There are two modes of operation for the resonant SWAP gate demonstrated in this Letter. First, a projection-SWAP can be used to transfer spin eigenstates Figure 1. (a) Charge stability map for a DQD formed using sites 3 and 4 in the quadruple dot array (inset). Quantum control is performed near the center of the (1,1) charge stability region as denoted by the green circle. Readout of dot 4 is performed at the (1,0)-(1,1) charge transition denoted by the blue triangle. (b) The typical measurement cycle is shown for controlling and reading out two quantum dots. In panel A, the qubits are manipulated and in panel B Q4 is read out through spin-selective tunneling -leaving the qubit in the |↓ state. In panel C, the exchange interaction J34 between Q3 and Q4 is modulated (through modulation of...

Coherent spin-state transfer via Heisenberg exchange

“…In the future, spin state transfer via Heisenberg exchange will work best in systems with small gradients and small levels of spin noise, such as silicon qubits. However, dynamically corrected gates [46] and resonant approaches [47,48] can also be used to implement highfidelity SWAP operations in the presence of gradients and noise.…”

Adiabatic electron charge transfer between two quantum dots in presence of 1/f noise

“…However, scaling up to large quantum circuits in architecture based on QDs will require mastering of long-distance quantum communication between registers of a few qubits [9][10][11][12]. While applying multiple SWAP gates [13][14][15] to subsequent spin qubits in a chain of quantum dots is the most conceptually straightforward proposal, the two most recently successful avenues for achieving this goal are either coherently coupling stationary spin qubits to flying qubits, specifically to microwave photons [16][17][18], or simply making electron spin qubits mobile in a controlled way. The latter can be achieved in polar materials such as GaAs with surface acoustic waves [19][20][21] making a single electron travel for up to 100 µm [20] distance, or by gate voltage controlled transfer of an electron along a chain of quantum dots.…”

Theoretical Study on Spin-Selective Coherent Electron Transfer in a Quantum Dot Array

“…On the other hand, the GaAs system can form a large dot, although the short coherence time is problematic [96]. The spin-orbit coupling [97,98] could be problematic in Step II. However, we believe that the study of clever pulse schemes to mitigate spin-orbit coupling is beyond the scope of the paper.…”