Coherent State Quantum Process Tomography

Norman Y. Yao, Chris R. Laumann, Alexey Vyacheslavovich Gorshkov +2 more

Xiang‐Bin Wang, Zong‐Wen Yu, Jiazhong Hu +2 more

An arbitrary quantum-optical process (channel) can be completely characterized by probing it with coherent states using the recently developed coherent-state quantum process tomography (QPT) [Lobino et al., Science 322, 563 (2008)]. In general, precise QPT is possible if an infinite set of probes is available. Thus, realistic QPT of infinite-dimensional systems is approximate due to a finite experimentally feasible set of coherent states and its related energy-cutoff approximation. We show with explicit formulas that one can completely identify a quantum-optical Gaussian process just with a few different coherent states without approximations like the energy cutoff. For tomography of multimode processes, our method exponentially reduces the number of different test states, compared with existing methods.

Kavan Kishore Modi, Cesar Rodriguez, Aik-meng Kuah +2 more

Aamir Anis, Alexander I. Lvovsky

Coherent-state quantum process tomography (csQPT) is a method for completely characterizing a quantum-optical ‘black box’ by probing it with coherent states and carrying out homodyne measurements on the output (Lobino et al 2008 Science 322 563). We present a technique for csQPT that is fully based on statistical inference, in particular, quantum expectation-maximization. The method relies on the Jamiolkowski isomorphism and iteratively reconstructs the process tensor in the Fock basis directly from the experimental data. This approach permits incorporation of a priori constraints into the reconstruction procedure, thereby guaranteeing that the resulting process tensor is physically consistent. Furthermore, our method is easier to implement and requires a narrower range of coherent states than its predecessors. We test its feasibility using simulations on several experimentally relevant processes.

Xiaohua Wu, Ke Xu

Aamir Anis, Alexander I. Lvovsky

Coherent-state quantum process tomography (csQPT) is a method of completely characterizing a quantum-optical "black box" by probing it with coherent states and performing homodyne measurements on the output [M. Lobino et al, Science 322, 563 (2008)]. We present a technique for csQPT that is fully based on statistical inference, specifically, quantum expectation-maximization. The method relies on the Jamiolkowski isomorphism and iteratively reconstructs the process tensor in the Fock basis directly from the experimental data. This approach permits incorporation of a priori constraints into the reconstruction procedure, thereby guaranteeing that the resulting process tensor is physically consistent. Furthermore, our method is easier to implement and requires a narrower range of coherent states than its predecessors. We test its feasibility using simulations on several experimentally relevant processes.