Oxford Physicists Achieve Record Accuracy in Quantum Qubit Control

Physicists at the University of Oxford have established a new world record for the accuracy of controlling a single quantum bit, or qubit, achieving an error rate of just 0.000015% – equivalent to one error in 6.7 million operations. This result, representing a significant improvement over the group’s previous benchmark set a decade ago, demonstrates an unprecedented level of precision in quantum control. Published this week in Physical Review Letters, the findings represent a crucial step towards realising robust and practical quantum computers capable of tackling complex calculations. The team’s success highlights the potential of trapped calcium ions as qubits, controlled in this instance not by conventional lasers, but by more stable and scalable electronic signals.

Record-Breaking Accuracy Achieved

Researchers at the University of Oxford have established a new global standard for single-qubit operational accuracy, achieving an error rate of 0.000015%, or one error in 6.7 million operations. This result represents a nearly ten-fold improvement over the group’s previous benchmark, set in 2014, and signifies substantial progress towards the realisation of robust and functional quantum computers. This reduction in error is critical for complex calculations, as millions of operations are required, and fewer redundant qubits are needed for error mitigation.

This advancement stems from a shift to electronic control mechanisms, offering substantial advantages in system stability and scalability compared to traditional laser systems. The implementation simplifies integration with ion trap chips, paving the way for more compact and efficient quantum processors. Notably, the experiment was conducted at room temperature and without the need for magnetic shielding, further reducing the technical demands of constructing a functional quantum computer.

The team’s prior expertise, demonstrated by achieving a 1 in 1 million error rate in 2014, underpinned the formation of Oxford Ionics in 2019, a leading developer of high-performance trapped-ion qubit platforms. However, it is crucial to note that single-qubit gate fidelity represents only one component of a functional quantum computer. Current two-qubit gate demonstrations still exhibit significantly higher error rates—approximately 1 in 2000—and reducing these rates is paramount to achieving fully fault-tolerant quantum computation.

Benefits for Quantum Computer Design

The achievement of a single-qubit error rate of 0.000015% directly impacts quantum computer design by reducing the infrastructural demands of error correction. Lower error rates translate to a decreased requirement for physical qubits to implement a given quantum algorithm, subsequently lowering the overall cost, size, and complexity of building a functional quantum computer. This is particularly beneficial for the development of ion trapping chips, a leading architecture for trapped-ion quantum computers.

The ease of integrating electronic control systems directly onto these chips facilitates miniaturisation and increased density of qubits, crucial for building powerful and compact quantum processors. Furthermore, the ability to operate the system at room temperature and without the need for magnetic shielding further streamlines the technical requirements, paving the way for more accessible and deployable quantum computing platforms. This contrasts with laser-based systems, which often require bulky external optics and precise alignment, hindering scalability.

Challenges Remain for Full Functionality

Despite achieving a record-breaking single-qubit error rate, substantial challenges remain in realising fully functional quantum computers. Current quantum architectures necessitate both single- and two-qubit gates operating in concert; however, two-qubit gate performance currently lags significantly behind, exhibiting error rates of approximately 1 in 2000 in leading demonstrations.

Addressing this disparity is critical for the development of fault-tolerant quantum machines. While minimising single-qubit errors reduces the overall error budget, the comparatively high error rate of two-qubit gates currently represents a major impediment to scaling quantum computations. Further research and innovation are therefore focused on improving the fidelity of these multi-qubit operations. Reducing two-qubit error rates will not only enhance the reliability of quantum calculations but also lessen the demands on error correction protocols, potentially simplifying the infrastructure required for practical quantum computing and reducing the number of physical qubits needed to implement a given algorithm.