Abstract
We propose a simple scheme to reduce readout errors in experiments on quantum systems with finite number of measurement outcomes. Our method relies on performing classical post-processing which is preceded by Quantum Detector Tomography, i.e., the reconstruction of a Positive-Operator Valued Measure (POVM) describing the given quantum measurement device. If the measurement device is affected only by an invertible classical noise, it is possible to correct the outcome statistics of future experiments performed on the same device. To support the practical applicability of this scheme for near-term quantum devices, we characterize measurements implemented in IBM's and Rigetti's quantum processors. We find that for these devices, based on superconducting transmon qubits, classical noise is indeed the dominant source of readout errors. Moreover, we analyze the influence of the presence of coherent errors and finite statistics on the performance of our error-mitigation procedure. Applying our scheme on the IBM's 5-qubit device, we observe a significant improvement of the results of a number of single- and two-qubit tasks including Quantum State Tomography (QST), Quantum Process Tomography (QPT), the implementation of non-projective measurements, and certain quantum algorithms (Grover's search and the Bernstein-Vazirani algorithm). Finally, we present results showing improvement for the implementation of certain probability distributions in the case of five qubits.
Highlights
In recent years, quantum technologies have been rapidly developing
In what follows we present results of the quantum state and quantum process tomographies performed on singlequbit systems and quantum state tomographies performed on two-qubit systems
We have presented a scheme for the mitigation of readout errors which is suitable for noisy and imperfect quantum devices
Summary
Quantum technologies have been rapidly developing. Scientists and engineers around the world share the hope and fascination caused by the possibility of creating devices that would allow for the manipulation of delicate quantum states with unprecedented precision [1]. Due to the advent of quantum cloud services (IBM [2, 3], Rigetti [4], DWave [5]), any researcher has a possibility to perform experiments on actual quantum devices. If one really hopes for utilizing such near-term devices for real-life applications such as quantum computation [6], quantum simulations [7] or generating random numbers [8], experimental imperfections must be taken into account. To properly characterize noise occurring in the devices and to develop error correction and mitigation schemes that may help to fight it have become tasks of fundamental importance [9, 10, 11, 12, 13, 14, 15].
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