Abstract
Physical qubits in experimental quantum information processors are inevitably exposed to different sources of noise and imperfections, which lead to errors that typically accumulate hindering our ability to perform long computations reliably. Progress towards scalable and robust quantum computation relies on exploiting quantum error correction (QEC) to actively battle these undesired effects. In this work, we present a comprehensive study of crosstalk errors in a quantum-computing architecture based on a single string of ions confined by a radio-frequency trap, and manipulated by individually-addressed laser beams. This type of errors affects spectator qubits that, ideally, should remain unaltered during the application of single- and two-qubit quantum gates addressed at a different set of active qubits. We microscopically model crosstalk errors from first principles and present a detailed study showing the importance of using a coherent vs incoherent error modelling and, moreover, discuss strategies to actively suppress this crosstalk at the gate level. Finally, we study the impact of residual crosstalk errors on the performance of fault-tolerant QEC numerically, identifying the experimental target values that need to be achieved in near-term trapped-ion experiments to reach the break-even point for beneficial QEC with low-distance topological codes.
Highlights
Quantum computation aims at manipulating delicate entangled states to achieve functionalities beyond those presented by classical devices
Scalable quantum error correction codes (QECCs) preserve quantum information by encoding it redundantly in a set of physical qubits [1] such that, in principle, arbitrary levels of protection can be achieved by increasing the number of redundant physical qubits while employing active detection and correction of errors, provided physical noise rates lie below the critical threshold of the corresponding QECC
It should be noted that our study focuses on a trapped-ion quantum processor and the example of the 7-qubit colour code, the error mitigation technique and analysis discussed here can be adapted to other quantum processor architectures, or other QECCs and algorithms
Summary
Quantum computation aims at manipulating delicate entangled states to achieve functionalities beyond those presented by classical devices. These new experimental capabilities include the possibility to perform high-fidelity entangling gates addressed on specific subsets of ions [46,47,48] , leading to effective all-to-all connectivity for two-qubit entangling gates These capabilities have motivated the study of the single-string ion trap scenario as a viable approach to implementing an operational logical qubit [8, 49]. For such low-distance codes, it is of primary importance to use faulttolerant (FT) circuit designs so that errors do not proliferate due to unsuitable circuit layouts, allowing to exploit the full correcting power of the QECC Such fault-tolerant circuit constructions will serve the purpose of reaching the breakeven point of the advantage of QEC in small devices and provide crucial information that can guide future strategies in progress towards largescale quantum computers.
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