Resource-efficient algorithm for estimating the trace of quantum state powers

• URL: http://arxiv.org/abs/2408.00314v2
• Date: Tue, 18 Feb 2025 08:33:10 GMT
• Title: Resource-efficient algorithm for estimating the trace of quantum state powers
• Authors: Myeongjin Shin, Junseo Lee, Seungwoo Lee, Kabgyun Jeong,
• Abstract summary: Estimating the trace of quantum state powers, $textTr(rhok)$, for $k$ identical quantum states is a fundamental task. We introduce an algorithm that requires only $mathcalO(tilder)$ qubits and $mathcalO(tilder)$ multi-qubit gates. We extend our algorithm to the estimation of $textTr(rhok)$ for arbitrary observables and $textTr(rhok)
• Score: 1.5133368155322298
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• Abstract: Estimating the trace of quantum state powers, $\text{Tr}(\rho^k)$, for $k$ identical quantum states is a fundamental task with numerous applications in quantum information processing, including nonlinear function estimation of quantum states and entanglement detection. On near-term quantum devices, reducing the required quantum circuit depth, the number of multi-qubit quantum operations, and the copies of the quantum state needed for such computations is crucial. In this work, inspired by the Newton-Girard method, we significantly improve upon existing results by introducing an algorithm that requires only $\mathcal{O}(\tilde{r})$ qubits and $\mathcal{O}(\tilde{r})$ multi-qubit gates, where $\tilde{r} = \min\left\{\text{rank}(\rho), \left\lfloor\ln\left({2k}/{\epsilon}\right)\right\rfloor\right\}$. Furthermore, we prove that estimating $\{\text{Tr}(\rho^i)\}_{i=1}^{\tilde{r}}$ is sufficient to approximate $\text{Tr}(\rho^k)$ even for large integers $k > \tilde{r}$. This leads to a rank-dependent complexity for solving the problem, providing an efficient algorithm for low-rank quantum states while also improving existing methods when the rank is unknown or when the state is not low-rank. Building upon these advantages, we extend our algorithm to the estimation of $\text{Tr}(M\rho^k)$ for arbitrary observables and $\text{Tr}(\rho^k \sigma^l)$ for multiple quantum states.

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