Experimental Simulation of Larger Quantum Circuits with Fewer Superconducting Qubits

Abstract

Although near-term quantum computing devices are still limited by the quantity and quality of qubits in the so-called NISQ era, quantum computational advantage has been experimentally demonstrated. Moreover, hybrid architectures of quantum and classical computing have become the main paradigm for exhibiting NISQ applications, where low-depth quantum circuits are repeatedly applied. In order to further scale up the problem size solvable by the NISQ devices, it is also possible to reduce the number of physical qubits by "cutting" the quantum circuit into different pieces. In this work, we experimentally demonstrated a circuit-cutting method for simulating quantum circuits involving many logical qubits, using only a few physical superconducting qubits. By exploiting the symmetry of linear-cluster states, we can estimate the effectiveness of circuit-cutting for simulating up to 33-qubit linear-cluster states, using at most 4 physical qubits for each subcircuit. Specifically, for the 12-qubit linear-cluster state, we found that the experimental fidelity bound can reach as much as 0.734, which is about 19% higher than a direct simulation on the same 12-qubit superconducting processor. Our results indicate that circuit-cutting represents a feasible approach of simulating quantum circuits using much fewer qubits, while achieving a much higher circuit fidelity.

Investigating the effect of circuit cutting in QAOA for the MaxCut problem on NISQ devices

“…The observed result that quantum circuit cutting applied in QAOA for the MaxCut problem produces execution results less affected by noise are in line with evaluations of circuit cutting on benchmark circuits [29,31,32]. The reasoning is that there is a range in the size of the subcircuits where their execution is significantly less noisy than the execution of the original circuit.…”

“…In circuit cutting experiments, various works have practically demonstrated that circuit cutting can be used to expand the size of executable circuits beyond the physical capabilities of NISQ devices, e.g., for a set of benchmark circuits [29], GHZ circuits [30], and circuits for linear cluster states [31]. Moreover, it has been shown experimentally that in noisy simulations and on NISQ devices, circuit cutting can lead to better, i.e.…”

“…Moreover, it has been shown experimentally that in noisy simulations and on NISQ devices, circuit cutting can lead to better, i.e. less noisy, execution results [29][30][31][32]. Circuit cutting can help with gate errors and short decoherence times since smaller circuits are less susceptible to these noise sources; in contrast, readout errors can be detrimental to the circuit cutting procedure since it requires additional measurements [32].…”

“…Quantum circuit cutting can be classified as a decomposition technique on the quantum circuit level as it is independent of the algorithm generating the circuits [14,15]. Like other decomposition approaches, it can reduce the number of required qubits and increase the size of solvable problem instances with available quantum devices [29,31]. However, our work focuses not on expanding the problem size but on decreasing circuit complexity.…”

“…On the other hand, the used circuit cutting approach must execute only 32 subcircuits for the two cuts. Other work focuses on experiments with more than two cuts [31,32] and also on significantly reducing the number of required subcircuits [40]. Regarding the selection of the NISQ devices, the experiments were conducted on multiple devices of IBM's Falcon chip architecture.…”