Amplification of quantum states and noiseless photon amplifiers

V. A. Andreev, Milena Davidović, Ljubica Davidović +2 more

Michal Neset, Jiří Fadrný, Martin Bielak +3 more

Noiseless quantum amplifiers are probabilistic quantum devices that enhance amplitude of coherent states without adding any noise, which has far reaching applications in quantum optics and quantum information processing. Here, we report on experimental implementation of an advanced noiseless quantum amplifier for coherent states of light that is based on conditional addition of two photons followed by conditional subtraction of two photons. We comprehensively characterize the noiselessly amplified coherent states via quantum state tomography and analyze the amplification gain and noise properties of the amplifier. We observe very good agreement between the experiment and theoretical predictions. Our work reveals that sequences of multiple photon additions and subtractions represent an efficient and experimentally feasible alternative to multiplexing that was originally proposed to boost the performance of noiseless quantum amplifiers. Beyond noiseless quantum amplification, our experiment represents a significant step forward towards engineering complex quantum operations on traveling light beams by coherent combinations of various sequences of multiphoton additions and subtractions.

B. Schr�der

Michal Neset, Jiří Fadrný, Martin Bielak +3 more

Noiseless quantum amplifiers are probabilistic quantum devices that enhance the amplitude of coherent states without adding any noise, which has far reaching applications in quantum optics and quantum information processing. Here, we report on an experimental implementation of an advanced noiseless quantum amplifier for coherent states of light that is based on the conditional addition of two photons followed by the conditional subtraction of two photons. We comprehensively characterize the noiselessly amplified coherent states via quantum state tomography and analyze the amplification gain and noise properties of the amplifier. We observe very good agreement between the experiment and theoretical predictions. Our work reveals that sequences of multiple photon additions and subtractions represent an efficient and experimentally feasible alternative to multiplexing that was originally proposed to boost the performance of noiseless quantum amplifiers. Beyond noiseless quantum amplification, our experiment represents a significant step forward towards engineering complex quantum operations on traveling light beams by coherent combinations of various sequences of multiphoton additions and subtractions.

Yangjing Wen, Jian Chen, Xianglin Yang

Michal Neset, Jiří Fadrný, Martin Bielak +3 more

Loss suppression is a major challenge in quantum communication and quantum computing, primarily due to the limitations imposed by the no-cloning theorem. We present a noiseless quantum amplifier capable of probabilistically increasing the amplitude of coherent states without introducing additional noise to the amplified state. This is achieved through the conditional addition and subtraction of photons. Previously, experimental photon addition was restricted to a single photon. Recently, we have pushed these boundaries, demonstrating photon addition of up to three photons for the first time [1], as well as the combination of conditional addition of two photons followed by their conditional subtraction [2]. Our advanced noiseless amplifier achieves high amplification gain, fidelity, and purity, with the quadrature variances of the noiselessly amplified coherent states remaining close to the minimum uncertainty limit. Figure 1 illustrates the performance of our amplifier compared to that of an amplifier based on single-photon addition and subtraction.