Shang Yu

Quantum control limited by quantum decoherence

We describe quantum controllability under the influences of the quantum decoherence induced by the quantum control itself. It is shown that, when the controller is considered as a quantum system, it will entangle with its controlled system and then cause quantum decoherence in the controlled system. In competition with this induced decoherence, the controllability will be limited by some uncertainty relation in a well-armed quantum control process. In association with the phase uncertainty and the standard quantum limit, a general model is studied to demonstrate the possibility of realizing a decoherence-free quantum control with a finite energy within a finite time. It is also shown that if the operations of quantum control are to be determined by the initial state of the controller, then due to the decoherence which results from the quantum control itself, there exists a low bound for quantum controllability.

Experimental implementation of a degenerate optical resonator supporting more than 46 Laguerre-Gaussian modes

Great efforts have been made to investigate photons orbital angular momentum (OAM) due to its comprehensive applications ranging from micro-manipulation to biosciences. Recently, it has been proposed that the unlimited OAM number can be used as synthetic degrees of freedom and can be used for quantum simulation. Here, we demonstrate a vital step in manipulating such kind of unlimited degree of freedom simultaneously. We construct an optical resonator with four spherical mirrors, which is predicted to support lights in different Laguerre-Gaussian modes with well-defined OAMs. The transmitted peaks of more than 46 Laguerre-Gaussian modes are observed to be overlapped within the bandwidth of the resonator. The transmitted beam profiles are further obtained by locking the resonator. Our experimental results establish the critical techniques to manipulate multiple-OAM degrees of freedom, which are useful for quantum simulation.