Quantum computers have entered the NISQ (noisy intermediate-scale quantum) era, revolutionizing the field of computing. These machines, equipped with tens to hundreds of noisy qubits, are already capable of implementing quantum operations and basic algorithms. Despite the absence of error correction, researchers are developing algorithms and techniques tailored to the strengths and limitations of these quantum devices, paving the way for non-classical computation in the near future. However, evaluating and comparing the performance of different quantum devices is crucial to selecting the most suitable one for specific computational tasks. This is where benchmarking protocols come into play, allowing for reproducible measurements of quantum device performance.
Benchmarking Quantum Devices
Benchmarking protocols go beyond assessing hardware characteristics and aim to capture the complexity of quantum machines. The goal is to design protocols that yield maximum information about a quantum device’s performance. Various benchmarking approaches have been proposed, including randomised benchmarking, cross-entropy benchmarks, and the quantum volume. These protocols not only consider hardware benchmarks but also application benchmarks that assess a quantum device’s performance based on its execution of different algorithms and applications.
The Vital Role of Entanglement
One of the fundamental applications used to benchmark quantum devices is the generation and verification of entanglement. Several tests of multipartite entanglement have been implemented, such as Mermin inequalities and multiparty Bell inequalities. These tests help evaluate the entanglement between qubits and verify the state generation of a large number of qubits. In this study, we focus on characterizing an IBM quantum computer with 27 superconducting qubits using a method called non-adaptive measurement-based quantum computation (NMQC).
NMQC involves computing a multivariate function using quantum correlations. Unlike local hidden variables (LHVs), which can only output linear functions, quantum correlations allow for the computation of all Boolean functions. The success of NMQC can be measured by the violation of a Bell inequality, indicating its advantage over classical resources. Previous implementations of NMQC with GHZ states have been limited to four photons. However, in this study, we utilize GHZ states on an IBM quantum computer to implement NMQC with more than four qubits, enabling us to test the quantum correlations and non-classical properties of the device.
Unveiling Multipartite Entanglement
We perform NMQC for various bit functions on the IBM Quantum System One (QSO), showcasing its ability to exhibit multipartite entanglement. For qubit numbers up to five, we employ quantum readout error mitigation to reduce local measurement errors. For higher qubit numbers, we take advantage of the error mitigation tools provided by Qiskit. Our results demonstrate violations of the associated Bell inequalities for up to seven qubits, providing further evidence of the non-classical properties of IBM’s quantum computing system.
Frequently Asked Questions (FAQ)
Q: What is NMQC?
A: Non-adaptive measurement-based quantum computation (NMQC) is a method that utilizes quantum correlations to compute multivariate functions and outperforms classical resources.
Q: How is NMQC different from classical computation?
A: NMQC can compute all Boolean functions, whereas classical computation restricted to LHVs can only output linear functions.
Q: What is entanglement?
A: Entanglement is a phenomenon in quantum physics where the state of one particle becomes correlated with the state of another particle, even when they are physically separated.
Q: Why is benchmarking important in quantum computing?
A: Benchmarking protocols allow for the evaluation and comparison of different quantum devices, helping researchers select the most suitable quantum computer for specific computational tasks.
Q: What is the significance of violating a Bell inequality?
A: The violation of a Bell inequality indicates the non-classical properties of a quantum computing system and demonstrates its advantage over classical resources.
– Quantum Computing and Quantum Information by Michael A. Nielsen and Isaac L. Chuang