Abstract
Density matrix, which characterizes a quantum state, plays an important role in quantum mechanics. Recently, a method which can directly measure the elements of a density matrix was proposed. Compared with the conventional quantum state tomography which is widely used to reconstruct the density matrix, this measurement method has the advantages of directness and simplicity. However, this direct measurement method relies on an extra pointer space. The addition of this extra pointer can increase the complexity of an experiment. In this paper, we first review previous work on direct measurement, then we propose a scheme to directly measure the density matrix based on <i>δ</i>-quench, which is also a direct measurement method but needs no additional pointer. This proposal reduces the complexity of the measuring system and further simplifies the measurement. We propose two schemes to realize this <i>δ</i>-quench measurement, then analyse their superiorities in different situations of measurement. An experiment to measure photon's density matrix is also designed.
Highlights
In this paper, we first review previous work on direct measurement, then we propose a scheme to directly measure the density matrix based on d-quench, which is also a direct measurement method but needs no additional pointer
We propose two schemes to realize this d-quench measurement, then analyse their superiorities in different situations of measurement
类似地, 先 用 QWP, HWP 和 BD 制备出路径量子比特的初 态
Summary
太赫兹辅助测量铷原子超快量子相干过程的理论研究 The theoretical study of terahertz-streaking photoionization for ultrafast imaging of density matrix in rubidium atom 物理学报. 最后, 波函数可以在指针态 的测量结果中被重构出来: 1 ⟨πx⟩w = sin α (⟨s |σx| s⟩ − i ⟨s |σy| s⟩) , (1) 中 Πj = |j⟩⟨j|为待测系统本征态 |j⟩的投影算符, σyA 则为指针 A 的 y 方向泡利算符, θA 为耦合强度.
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