Experimental Noiseless Quantum Amplification of Coherent States of Light by Two-Photon Addition and Subtraction

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.