A general method for solving an important class of quantum detection problems will be presented and evaluated. The quantum theory for detecting pure states for communications purposes has been developed over two decades ago, however the mixed state problem representing signal plus noise states has received little attention due to its great complexity. Here we develop a practical model for solving the mixed-state problem using a discrete approximation to the coherent-state representation of signal plus noise density operators.
A general method for solving an important class of quantum detection problems will be presented and evaluated. The quantum theory for detecting pure states for communications purposes has been developed over two decades ago, however the mixed state problem representing signal plus noise states has received little attention due to its great complexity. Here we develop a practical model for solving the mixed-state problem using a discrete approximation to the coherent-state representation of signal plus noise density operators.
A new technique for evaluating the performance of quantum signals observed in the presence noise is described and evaluated. The quantum theory for detecting coherent-state signals has been developed previously, however the quantum "signal plus noise" problem has received little attention due to its complexity. Here we develop a discrete approximation to the coherent-state representation of signal-plus-noise density operators, and present solutions to optimum receiver performance in terms of quantum "measurement states" whose performance is optimized via generalized rotations in Hilbert space. An efficient algorithm for carrying out the required numerical optimization is described and applied to binary signals observed in the presence of noise, for which exact results are available for comparison. The algorithm is then applied to the detection of ternary signals observed in the presence of noise, a previously unsolved problem, and the performance of the optimum receiver characterized.
A new technique for evaluating the performance of quantum signals observed in the presence of noise is described and evaluated. The quantum theory for detecting coherent-state signals has been developed previously; however, the quantum signal-plus-noise problem has received little attention due to its complexity. Here we develop a discrete approximation to the coherent-state representation of signal-plusnoise density operators, and present solutions to optimum receiver performance in terms of quantum measurement states whose performance is optimized via generalized rotations in Hilbert space. An efficient algorithm for carrying out the required numerical optimization is described and applied to binary signals observed in the presence of noise, for which exact results are available for comparison. The algorithm is then applied to the detection of ternary signals observed in the presence of noise, a previously unsolved problem, and the performance of the optimum receiver is characterized.
A method is given for calculating the minimum average error probability attainable in deciding between a mixed state and a pure state of a quantum system. It is applied, first, to the detection of a noisy coherent pulse represented by a state with a Gaussian P-representation and, second, to the detection of a signal represented at the transmitter by a two-photon coherent state (TCS). In both problems the field of the receiver is free of background noise and, when no signal was transmitted, is in the ground state.
Quantum detection techniques based on multi-access quantum channel promise efficient quantum optimal solutions to quantum multi-user detection. "Discrete coherent state"(DCS) approximation method is a practical model for solving the mixed-state detection problem. Generally, the input states are pure states, while the output states are turned out to be mixed states corrupted by the noise in quantum channel. In this paper, we consider the detection scheme with DCS approximation in a quantum multiple access channel. We deduce the error probability of symbol rate of the detection algorithm with DCS detection scheme in multi-user detection fashion. By numerical simulations, we analyze and compare the performance of this detection scheme with different degree approximation. It is shown that this detection scheme is available for the quantum multi-user detection. For a normal noise, say jV=0.1, we will get the 10-3when number of photons Ns go to 18.
Multi-user detection (MUD) techniques will be adopted in the future wired and wireless communication system. It is known that quantum detection techniques promise efficient optimal solutions to this NP (non-polynomial) hard problem in classical domain. "Discrete coherent state"(DCS) approximation method is a practical model for solving the mixed-state detection problem. In this paper, we use DCS approximation model for the MUD problem. For a noisy quantum channel, it is feasible to consider the output states are mixed states, which are the input pure states corrupted by the noise when the pure states pass thought the noisy quantum channel. For simplicity and generality, we deduce the error probability of symbol against correlation coefficient in two users' fashion. By numerical simulations, we analyze and compare the performance of this representation. The simulation results show that the detection error will increase while the correlation coefficient increase, and the performance is also effected by the noise level. With less noise, the system will get better performance. The DCS approximation representation is a good detection scheme for quantum multi-user detection.