Abstract
A fault-tolerant quantum processor may be configured using stationary qubits interacting only with their nearest neighbours, but at the cost of significant overheads in physical qubits per logical qubit. Such overheads could be reduced by coherently transporting qubits across the chip, allowing connectivity beyond immediate neighbours. Here we demonstrate high-fidelity coherent transport of an electron spin qubit between quantum dots in isotopically-enriched silicon. We observe qubit precession in the inter-site tunnelling regime and assess the impact of qubit transport using Ramsey interferometry and quantum state tomography techniques. We report a polarization transfer fidelity of 99.97% and an average coherent transfer fidelity of 99.4%. Our results provide key elements for high-fidelity, on-chip quantum information distribution, as long envisaged, reinforcing the scaling prospects of silicon-based spin qubits.
Highlights
A fault-tolerant quantum processor may be configured using stationary qubits interacting only with their nearest neighbours, but at the cost of significant overheads in physical qubits per logical qubit
Strategies for quantum information transfer in semiconductor spin qubits include sequential application of spin SWAP gates[25,26,27], coherent coupling of stationary qubits mediated by flying qubits such as photons in a cavity[28,29,30] or, as proposed in the literature[31,32] and explored here experimentally, physically transporting the particle that harbors the quantum information from one site to another[33,34,35,36,37,38]
In a longer chain of quantum dots, spin transport may be achieved by consecutive adiabatic tunneling between nearest neighbors
Summary
A fault-tolerant quantum processor may be configured using stationary qubits interacting only with their nearest neighbours, but at the cost of significant overheads in physical qubits per logical qubit. A popular strategy based on the 2D surface code[3] requires only nearest-neighbor operations between physical qubits with a very lenient error threshold These advantages, come at the cost of severe overheads in the number of physical qubits per logical qubit and the need for resource-intensive magic state distillation to achieve universal quantum logic. We discuss the limitations to the transfer fidelity based on these demonstrations as well as on dynamical decoupling efficacy and transfer time dependence This transfer method can be extended to longer quantum-dot chains by sequencing it from one site to the in a bucket-brigade manner, offering micron-scale on-chip quantum links for silicon spin-qubit architectures
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