Heralded noiseless linear amplification and distillation of entanglement

Signal amplification is ubiquitous in the control of physical systems, and the ultimate performance limit of amplifiers is set by quantum physics. Increasing the amplitude of an unknown quantum optical field, or any harmonic oscillator state, must introduce noise1. This linear amplification noise prevents perfect copying of the quantum state2, enforces quantum limits on communications and metrology3, and is the mechanism preventing the increase of entanglement via local operations. Non-deterministic versions of ideal cloning4 and local entanglement increase (distillation)5 are allowed, suggesting the possibility of non-deterministic noiseless linear amplification. Here we introduce, and experimentally demonstrate, such a noiseless linear amplifier for quantum states of the optical field, and use it for distillation of field-mode entanglement. This simple but powerful circuit enables practical devices for enhancing quantum technologies. The idea of noiseless amplification unifies approaches to cloning and distillation, and will find applications in quantum metrology and communications. A noiseless linear amplifier for quantum states of an optical field is demonstrated. The amplifier is also used to enhance entanglement through a technique known as distillation. Such amplification and distillation may be useful for quantum cloning, metrology and communications.