Digital quantum simulation of squeezed states via enhanced bosonic encoding in a superconducting quantum processor

TL;DR

This paper introduces a digital method for simulating squeezed states on superconducting qubits using enhanced bosonic encoding and variational protocols, achieving high-fidelity results despite hardware noise.

Contribution

It presents a novel Gray-code-based encoding strategy and resource optimization for simulating continuous-variable quantum states on qubit platforms.

Findings

Successful simulation of squeezed states with levels exceeding Fock space limits

High-fidelity state preparation confirmed by tomography and Wigner analysis

Demonstration of efficient bosonic encoding on superconducting hardware

Abstract

We present a fully digital approach for simulating single-mode squeezed states on a superconducting quantum processor using an enhanced bosonic encoding strategy. By mapping up to 2^{n} photonic Fock states onto n qubits, our framework leverages Gray-code-based encodings to reduce gate overhead compared to conventional one-hot or binary mappings. We further optimize resource usage by restricting the simulation on Fock states with even number of photons only, effectively doubling the range of photon numbers that can be represented for a given number of qubits. To overcome noise and finite coherence in current hardware, we employ a variational quantum simulation protocol, which adapts shallow, parameterized circuits through iterative optimization. Implemented on the Zuchongzhi-2 superconducting platform, our method demonstrates squeezed-state dynamics across a parameter sweep from vacuum state preparation (r=0) to squeezing levels exceeding the Fock space truncation limit (r>1.63). Experimental results, corroborated by quantum state tomography and Wigner-function analysis, confirm high-fidelity state preparation and demonstrate the potential of Gray-code-inspired techniques for realizing continuous-variable physics on near-term, qubit-based quantum processors.