A way to distinguish quantum noise

Tian Chen, Xiong Zhang, Xiangdong Zhang

Quantum walk (QW) provides a versatile platform for the realization of quantum algorithms. Due to the existence of the inevitable noises in the walk, the different quantum algorithms accommodating to different noises are demanded. Thus, the success of the algorithms based on the QW requires us to sense different noises in the walk. Until now, the way to distinguish different noises in the walk has been discussed rarely. Here, we propose an efficient way to sense the noises in the one and two dimensional QWs. The populations of the coin in the walk with or without decoherence are presented. By only detecting the populations of the coin in the QW, we can determine whether there exists the decoherence in the total QW system. Moreover, the non-Markovianity of the coin in the one and two dimensional QWs is revealed, in which the coin is taken as an open quantum system, and the other components of the QW system is taken as the large environment. With the measured value of the non-Markovianity for the coin, we can conjecture which kinds of noise emerges in the one and two dimensional QWs.

Daniele Cuomo

Malin Premaratne, Govind P. Agrawal

Virginie Dallot, Philippe B. Gallion

Summary form only given. Papers have evaluated the intensity noise at linear phase-insensitive optical amplifier output and identified it as amplified spontaneous emission (ASE). The contribution of input fluctuations and of the amplifier in output noise are not distinguishable, making impossible a description of squeezed-state amplification. Starting from a corpuscular approach of light and using Rice description of a coherent electromagnetic field, a new classical approach of intensity noise in amplifiers is proposed. It distinguishes the different sources of noise and evaluates their contribution in an intuitive but rigorous way. It also brings to the fore the effects of loss, intrinsic to the amplifier, in the intensity noise generation process. After reminding the corpuscular formalism of intensity noise and Rice representation of noise, the intensity noise at the output of linear, phase-insensitive optical amplifiers is deduced, followed by a reevaluation of the noise figure.

Guanru Feng, Joel J. Wallman, Brandon Buonacorsi +6 more

To exploit a given physical system for quantum information processing, it is critical to understand the different types of noise affecting quantum control. Distinguishing coherent and incoherent errors is extremely useful as they can be reduced in different ways. Coherent errors are generally easier to reduce at the hardware level, e.g., by improving calibration, whereas some sources of incoherent errors, e.g., T_{2}^{*} processes, can be reduced by engineering robust pulses. In this work, we illustrate how purity benchmarking and randomized benchmarking can be used together to distinguish between coherent and incoherent errors and to quantify the reduction in both of them due to using optimal control pulses and accounting for the transfer function in an electron spin resonance system. We also prove that purity benchmarking provides bounds on the optimal fidelity and diamond norm that can be achieved by correcting the coherent errors through improving calibration.

Ramón Alonso‐Sanz