Project: Controlling Spins in Quantum systems in an Online Setting

Acronym	ConSpiQuOS
Duration	01/08/2022 - 31/07/2025
Project Topic	Semiconducting spin qubits have small sizes and incredible operation speeds, but using them for large-scale fault-tolerant applications has so far been prevented by material noise limiting qubit coherence and decreasing gate fidelity. However, their strong sensitivity to electric fields can be profited from if a sufficiently large number of gate voltages can be adjusted accurately (low-frequency control) and tuned quickly (high-frequency control) to cancel noise. By integrating low-noise control electronics with on-hardware real-time signal generation as well as fast qubit readout, and applying the resulting control pulses to multi-channel state-of-the-art spin-qubit processors, we will for the first time perform conditional quantum logic in which the control feedback happens faster than the coherence times associated with the qubits. We will demonstrate this “online control” by performing the world’s first unconditional quantum teleportation of a spin qubit. Since online qubit control is a crucial ingredient of quantum error correction in fault-tolerant architectures, our breakthrough will be an important stepping stone toward successful scaling up of spin-qubit quantum information processors. To achieve such online quantum control with high fidelities, we take advantage of the unique specializations of the ConSpiQuOS partners. Through the development of tailored quantum algorithms (NTNU, ranging from neural networks for multi-qubit classification to qubit stabilization based on real-time Hamiltonian estimation), their implementation on acquisition and control hardware (QM, based on advanced FPGA-based high-frequency digitizers and generators), and the fabrication of a quantum-classical interface (QDV, multi-channel high frequency cryogenic sample holders controlled with room temperature electronics), will allow us to employ the readily available spin-qubit devices (UCPH) as small scale quantum processors. In year 1 we will acquire simultaneous single-shot readouts of multiple qubits (classified online by feeding high-frequency reflectometry signals into neural networks), from which we will monitor and estimate the (predominantly low-frequency) noise in each spin-qubit. Doing this in real-time allows universal multi-qubit control and access to the qubit-qubit noise correlations, which we will use to demonstrate dramatically improved coherence times. The real-time knowledge of the multi-qubit Hamiltonian parameters as well as a detailed understanding of the noise will be used to implement real-time feedback in year 2, optimizing single- and two-qubit gate fidelity by adjusting the control pulses. To show direct relevance for ongoing state-of-the-art progress to players developing quantum computers based on spin-qubits, we will in year 3 apply our results to perform unconditional quantum state teleportation based on a classical information channel.
Network	QuantERA II
Call	QuantERA II Call 2021

Project partner

Number	Name	Role	Country
1	QDevil ApS	Coordinator	Denmark
2	Niels Bohr Institute, University of Copenhagen	Partner	Denmark
3	Quantum Machines	Partner	Israel
4	Norwegian University of Science and Technology	Partner	Norway