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 noise(1). This linear amplification noise prevents perfect copying of the quantum state(2), enforces quantum limits on communications and metrology(3), and is the mechanism preventing the increase of entanglement via local operations. Non-deterministic versions of ideal cloning(4) 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.