Zaw Lin Htoo
<a href="https://ror.org/01mgdzc49">Centre for Quantum Technologies</a>, <a href="https://ror.org/01tgyzw49">National University of Singapore</a>, 3 Science Drive 2, Singapore 117543.
Phys Rev Lett. 2024 Aug 2;133(5):050201. doi: 10.1103/PhysRevLett.133.050201.
In circuit and cavity quantum electrodynamics devices where control qubits are dispersively coupled to high-quality-factor cavities, characteristic functions of cavity states can be directly probed with conditional displacement (CD) gates. In this Letter, I propose a method to certify non-Gaussian entanglement between cavities using only CD gates and qubit readouts. The CD witness arises from an application of Bochner's theorem to a surprising connection between two negativities: that of the reduced Wigner function, and that of the partial transpose. Non-Gaussian entanglement of some common states, like entangled cats and photon-subtracted two-mode squeezed vacua, can be detected by measuring as few as four points of the characteristic function. Furthermore, the expectation value of the witness is a simultaneous lower bound to the Wigner negativity volume and a geometric measure of entanglement conjectured to be the partial transpose negativity. Both negativities are strong monotones of non-Gaussianity and entanglement, respectively, so the CD witness provides experimentally accessible lower bounds to quantities related to these monotones without the need for tomography on the cavity states.
在控制量子比特与高品质因子腔色散耦合的电路和腔量子电动力学装置中，腔态的特征函数可以通过条件位移（CD）门直接探测。在本信函中，我提出了一种仅使用CD门和量子比特读出操作来验证腔之间非高斯纠缠的方法。该CD见证源于将博赫纳定理应用于两个负性之间的惊人联系：即约化维格纳函数的负性和部分转置的负性。通过测量特征函数的少至四个点，就可以检测一些常见态的非高斯纠缠，如纠缠猫态和光子扣除双模压缩真空态。此外，见证的期望值同时是维格纳负性体积的下界以及一种被推测为部分转置负性的纠缠几何度量的下界。这两个负性分别是非高斯性和纠缠的强单调量，因此CD见证为与这些单调量相关的量提供了实验上可获取的下界，而无需对腔态进行层析成像。
