Dynamical Error Reshaping Suppresses Transmon Noise in Dual-Rail Erasure Qubits by Two Orders of Magnitude

Erasure qubits represent a potentially transformative approach to quantum computing, promising to significantly reduce the resources required to build practical machines. Filippos Dakis, Sophia E. Economou, and Edwin Barnes, all from Virginia Tech’s Department of Physics, have now addressed a key obstacle to realising this potential, namely the noise introduced by the supporting components necessary for operating these qubits. The team demonstrates a method for reshaping dynamical errors, effectively suppressing noise during crucial erasure checks and two-qubit gate operations. This innovative control scheme reduces erasure check errors by a factor of one hundred and lowers the failure rate of logical two-qubit gates by up to one thousand, representing a substantial step towards fault-tolerant quantum computation with erasure qubits.

Several recent experiments demonstrate erasure qubits in superconducting quantum processors, most notably the dual-rail qubit defined by the one-photon subspace of two coupled cavities. A significant challenge lies in the noise introduced by ancillary components needed to perform erasure checks and two-qubit gates. This work demonstrates how to suppress these adverse effects while performing these critical operations, presenting control schemes that reduce erasure check errors by up to two orders of magnitude and substantially reduce the infidelity of logical two-qubit gates.

Dynamically Corrected Entangling Gate via Joint Parity Measurement

Scientists have developed a robust method for creating a high-fidelity entangling gate, specifically a ZZ gate, resilient to noise, particularly dephasing and crosstalk. Their approach leverages a joint-parity measurement between two data qubits and an ancilla qubit, projecting the system into a subspace where entanglement can be created. The team employs dynamic correction techniques, such as carefully designed pulse sequences, to actively suppress noise during the gate operation. A key element of this work is the use of dual rail encoding, which distributes quantum information across two physical qubits, providing inherent error resilience.

The ZZ gate, a fundamental building block for many quantum algorithms, is created by applying a phase flip to both qubits only if both are in the |1 state. The team utilizes superconducting quantum control, shaping control pulses to cancel out specific types of noise. The joint parity measurement measures the parity of the data qubits and the ancilla qubit, enabling entanglement. The team represents qubit states geometrically using the Bloch sphere, carefully controlling the torsion of the control pulse trajectory to achieve noise suppression. This work demonstrates how to construct the ZZ gate from a robust joint-parity unitary, enabling a logical ZZ gate on the dual rail qubits. This research is significant because it addresses a critical challenge in quantum computing: building robust and reliable quantum gates, potentially improving the performance and practicality of quantum computers.

Erasure Qubit Noise Suppression Achieved Dynamically

Scientists have achieved substantial suppression of noise affecting erasure qubits, a promising approach to reduce the resources needed for quantum computation. Their work focuses on mitigating the detrimental effects of noise from ancillary components during erasure checks and two-qubit gate operations. Experiments demonstrate a novel control scheme that reduces erasure check errors by two orders of magnitude. The team developed a dynamically corrected joint parity unitary, achieving a substantial reduction in logical two-qubit gate infidelities, up to three orders of magnitude. This improvement stems from a composite sequence designed to cancel dephasing noise to first order, resulting in a gate infidelity that scales with the fourth power of the noise strength. Measurements confirm that the dynamically corrected gate exhibits quartic sensitivity to dephasing, demonstrating a significant reduction in error rates. The research involved a carefully designed sequence of operations, including decoupling cavities, swapping photons, and applying conditional rotations, all optimized to minimize the impact of ancilla dephasing.

Erasure Qubit Fidelity Via Dynamical Decoupling

Researchers have achieved significant improvements in the performance of erasure qubits, a promising approach to reduce the resources needed for quantum computation. Their work focuses on dual-rail erasure qubits implemented using superconducting circuits, addressing noise introduced from ancillary components. By developing control schemes grounded in the principles of dynamical decoupling, the team successfully suppressed errors during erasure checks and two-qubit gates, reducing them by up to two orders of magnitude. These advancements stem from the design of pulses that actively counteract both static dephasing noise and crosstalk. The resulting gates exhibit not only higher fidelity but also reduced sensitivity to drifts in the frequencies of the transmon qubits, simplifying calibration procedures. Maintaining erasure bias throughout operations has the potential to accelerate quantum error correction decoding and lower overall computational overhead.