用低深度量子电路模拟流体动力学的非线性碰撞过程,无需额外量子比特即可实现耗散与非线性。
Surrogate Quantum Circuit Design for the Lattice Boltzmann Collision Operator
- 通过量子态编码与测量协议设计,自然生成非幺正动力学。
- 在IBM Heron上仅需724个原生门,且不依赖网格规模。
- 适合量子流体模拟研究者,可直接用于涡旋衰减等基准测试。
本研究提出一种学习低深度代理量子电路(SQC)的框架,用于近似格子玻尔兹曼方法(LBM)中D2Q9格子的非线性、耗散性且非幺正的Bhatnagar-Gross-Krook(BGK)碰撞算子。通过合理选择量子态编码、电路架构和测量协议,非幺正动力学可在物理概率空间中自然出现。该方法无需依赖辅助量子比特或后选择的随机算法来再现耗散,也无需多个状态副本捕捉非线性。所设计的SQC保留了BGK算子的关键物理性质,包括质量守恒、尺度协变性和D8对称性,动量守恒则通过训练损失中的惩罚项加以鼓励。当编译至IBM Heron量子处理器的原生门集时,假设全连接量子比特,电路仅需724个原生门,并在速度寄存器上局部运行,与格子大小无关。在泰勒-格林涡旋衰减和盖驱动腔两个基准案例上验证了SQC的准确性,成功复现涡旋衰减与流动回流现象。尽管当前集成SQC至量子LBM框架仍需每步测量与重初始化,但已提出迈向无测量形式的关键步骤。
原文摘要 · Abstract (English)
This study introduces a framework for learning a low-depth surrogate quantum circuit (SQC) that approximates the nonlinear, dissipative, and hence non-unitary Bhatnagar-Gross-Krook (BGK) collision operator in the lattice Boltzmann method (LBM) for the D2Q9 lattice. By appropriately selecting the quantum state encoding, circuit architecture, and measurement protocol, non-unitary dynamics emerge naturally within the physical population space. This approach removes the need for probabilistic algorithms relying on any ancilla qubits and post-selection to reproduce dissipation, or for multiple state copies to capture nonlinearity. The SQC is designed to preserve key physical properties of the BGK operator, including mass conservation, scale equivariance, and D8 equivariance, while momentum conservation is encouraged through penalization in the training loss. When compiled to the IBM Heron quantum processor's native gate set, assuming all-to-all qubit connectivity, the circuit requires only 724 native gates and operates locally on the velocity register, making it independent of the lattice size. The learned SQC is validated on two benchmark cases, the Taylor-Green vortex decay and the lid-driven cavity, showing accurate reproduction of vortex decay and flow recirculation. While integration of the SQC into a quantum LBM framework presently requires measurement and re-initialization at each timestep, the necessary steps towards a measurement-free formulation are outlined.
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