Universal control of a six-qubit quantum processor in silicon

Abstract

Future quantum computers capable of solving relevant problems will require a large number of qubits that can be operated reliably. However, the requirements of having a large qubit count and operating with high-fidelity are typically conflicting. Spins in semiconductor quantum dots show long-term promise but demonstrations so far use between one and four qubits and typically optimize the fidelity of either single-or two-qubit operations, or initialization and readout. Here we increase the number of qubits and simultaneously achieve respectable fidelities for universal operation, state preparation and measurement. We design, fabricate and operate a six-qubit processor with a focus on careful Hamiltonian engineering, on a high level of abstraction to program the quantum circuits and on efficient background calibration, all of which are essential to achieve high fidelities on this extended system. State preparation combines initialization by measurement and real-time feedback with quantum-non-demolition measurements. These advances will allow for testing of increasingly meaningful quantum protocols and constitute a major stepping stone towards large-scale quantum computers.

High fidelity state preparation, quantum control, and readout of an isotopically enriched silicon spin qubit

“…Past experiments demonstrating high fidelity control of LD spin qubits were generally limited to V ≈ 70-80% [21,35,36]. Recent experiments on a six qubit device achieved V = 93.5 -98% [15]. Here we demonstrate the integrated high performance of our device.…”

“…GST and IRB are implemented to demonstrate average single qubit gate fidelities exceeding 99.95% under the same operating conditions. Elzerman readout of larger LD spin qubit arrays [12,15,30,41] will require a reduction of the measurement time relative to the spin relaxation time. Furthermore, faster readout protocols will be necessary to fully unlock the potential of feedback-based error correction protocols [42].…”

“…In order for a qubit platform to be a serious contender for quantum information processing it must be able to demonstrate all of the DiVincenzo criteria for quantum computing with high fidelity. While singleand two-qubit gates implemented in Si have made steady progress, state preparation and measurement (SPAM) fidelities have generally been well below 90%, with a few recent exceptions [12][13][14][15]. To implement quantum error correction and realize fault tolerant operation the total logical error rate, which includes SPAM, must be kept low 2% [16].…”

Analog Quantum Simulation of the Dynamics of Open Quantum Systems with Quantum Dots and Microelectronic Circuits

“…While the quantum hardware operates at cryogenic temperatures, by controlling energy level spacing it can be made to simulate dynamics at arbitrary target temperatures. Recent advances in constructing fully controllable quantum dots with 6-10 individual quantum dot units [46,47] open a clear path toward the simulation of many-level systems. The concept can be further extended to anharmonic environments by introducing nonlinear circuit elements such as Josephson junctions.…”

“…State-of-the-art experiments using QDs involve the manipulation of up to 9 QDs in a linear geometry. [46,47] Recent experimental achievements include quantum teleportation between distant electron spins, [48] rapid shuttling of single electron across a large QD array [46] and even analog quantum simulation of strongly correlated electron systems, [49] all demonstrating the high controllability of the QD platform. These technical advances have positioned the QDs as an excellent candidate for analog quantum simulation.…”