We present a systems theory approach to the proof of a result bounding the required level of added quantum noise in a phase-insensitive quantum amplifier. We also present a synthesis procedure for constructing a quantum optical phaseinsensitive quantum amplifier which adds the minimum level of quantum noise and achieves a required gain and bandwidth. This synthesis procedure is based on a singu...

Reading: For the quantum theory of beam splitters: • C.C. Gerry and P.L. Knight, Introductory Quantum Optics (Cambridge University Press, Cambridge, 2005) Sect. 6.2. For the quantum theory of linear amplifiers: • C.M. Caves, “Quantum limits on noise in linear amplifiers,” Phys. Rev. D 26, 1817–1839 (1982). • L. Mandel and E. Wolf, Optical Coherence and Quantum Optics (Cambridge University Press...

Using a flow chart representation of quantum optomechanical dynamics, we design coherent quantum-noise-cancellation schemes that can eliminate the backaction noise induced by radiation pressure at all frequencies and thus overcome the standard quantum limit of force sensing. The proposed schemes can be regarded as novel examples of coherent feedforward quantum control.

The unavoidable presence of noise is thought to be one of the major problems to solve in order to pave the way for implementing quantum information technologies in realistic physical platforms. However, here we show a clear example in which noise, in terms of dephasing, may enhance the capability of transmitting not only classical but also quantum information, encoded in quantum systems, throug...

In this paper we consider adversarial noise models that will fail quantum error correction and fault-tolerant quantum computation. We describe known results regarding high-rate noise, sequential computation, and reversible noisy computation. We continue by discussing highly correlated noise and the “boundary,” in terms of correlation of errors, of the “threshold theorem.” Next, we draw a pictur...

Most of the existing studies are devoted to the quantum Zeno and anti-Zeno effects in open quantum systems under quantization environment; little attention has been paid to the quantum zeno dynamics behavior under classical noise. In this paper, we analyze the quantum Zeno and anti-Zeno dynamics under the random telegraph noise and the family of low-frequency noise with 1 f ⁄ spectrum. Based on...

This is a brief description of how to protect quantum states from dissipation and decoherence that arise due to uncontrolled interactions with the environment. We discuss recoherence and stabilisation of quantum states based on two techniques known as “symmetrisation” and “quantum error correction”. We illustrate our considerations with the most popular quantum-optical model of the system-envir...

In semiclassical theory, light is a classical electromagnetic wave and the fundamental source of photodetection noise is the shot effect arising from the discreteness of the electron charge. In quantum theory, light is a quantum-mechanical entity and the fundamental source of photodetection noise comes from measuring the photon-flux operator. The Glauber coherent states are Gaussian quantum sta...

Noise plays a uniquely informative role in connection with the particle-wave duality. It was Albert Einstein who first realized (in 1909) that electromagnetic fluctuations are different if the energy is carried by waves or by particles. The magnitude of energy fluctuations scales linearly with the mean energy for classical waves, but it scales with the square root of the mean energy for classic...

It is often said that the strength of quantum computation lies in the phenomena of quantum superposition and quantum entanglement. These features of quantum computation allow to perform the computation on all possible inputs that fit to the quantum register. One of the greatest achievements in the theory of quantum algorithms is quantum search algorithm introduced by Grover. The detailed descri...