arXiv subjects

Zhuoran Bao

Publications and source records attributed to Zhuoran Bao.

4 recordsLinked to original sources

arXiv2026

Bell State Analysis Provides an Optimal Basis Saturating the Quantum Cramer-Rao in Rotation Sensing

The second-order anti-coherent state of light is known to saturate the Cramer-Rao Bound (QCRB) for rotation sensing around an arbitrary axis. However, due to the complexity of the state and the inefficiency of state tomography, parameter extraction remains an open problem. In this manuscript, we approach the problem of parameter extraction using pairwise Bell state analysis with an additional path degree of freedom. Due to the transformation property of rotation, only the symmetric Bell states will show up in projection in the final state. We exploit this advantage to develop a scheme for extracting the rotation angle for N=4 and N=6 second-order anti-coherent states.

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arXiv2026

Quantum Sensing and Quantum Error Correction: Two Sides of the Same Coin

Quantum metrology has been making amazing progress in the past decades. It is always in researchers' interest to search for new optimal states that improve parameter estimation. In this paper, we point out a connection between the code's error correcting capacity and its ability to act as a sensor. We backed our claim by providing an example that relates the Absorption emission code to the sensor state for arbitrary state rotation. It is hoped that, in building such a unified theory, one can draw inspiration from error correction to develop promising quantum sensors.

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arXiv2026

Creating Qubit States with Degenerate Two-level Systems

A qubit, or quantum bit, is conventionally defined as "a physical system for storing information that is capable of existing in either of two quantum states or in a superposition of both". In this paper, we examine the simple question of whether two distinct levels, each consisting of multiply degenerate sub-states, could serve as a practical quantum bit. We explore this idea using a well-characterized atomic system of the kind employed in several quantum computing implementations. We approximate the atom as a two-level system without degeneracy lifting in the magnetic quantum number while using the angular momentum addition rules to select the desired state transition. We find that, in the continuous presence of the field, the atom still undergoes Rabi oscillations, which are suitable for quantum gate construction. In addition, we compute the average fidelity in quantum gate performance for a single degenerate atom and postulate the required form of two-atom interaction to construct a controlled Z gate.

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arXiv2025

Ancilla-Assisted Process Tomography with Bipartiete Mixed Separable States

It has been shown that the entanglement between the system and ancillary states is not a strict requirement for performing ancilla-assisted process tomography(AAPT). Instead, from a theoretical point of view, it only requires that the system-ancilla state be faithful, which, in the qubit case, is the invertibility of a certain matrix representing the state. Our paper takes on the operational definition of faithfulness, i.e., a state is faithful if one can extract complete information about the quantum process, and we restrict the process to single-qubit operations on a two-qubit system-ancilla state. We present a theoretical analysis that connects the invertibility problem to the concept of Sinisterness, which quantifies the correlation between two qubits and can be generalized to bipartite systems formed by qubits for a certain class of states. Using Sinisterness, we derive a way of constructing two-qubit states that are guaranteed to be faithful and estimate the bound on the average error of the process featured by the condition number. Our analysis agrees that the maximally entangled states provided the smallest error amplification. Nevertheless, it maps out a numerical region where the advantage of the entanglement starts.

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