Distinguishing Between Optical Coherent States at the Fundamental Quantum Limit

Dr. JM Geremia

Department of Physics and Astronomy, University of New Mexico, Albuquerque

Especially in the optical sciences, we spend a lot of time working with coherent states of light- they represent the quantum states of the electromagnetic field generated by a laser. Unfortunately, quantum mechanics makes it impossible to distinguish perfectly between coherent states with different amplitudes (i.e., different values of their average intensity or phase). In fact, any measurement we might perform to determine whether an optical field is described by one amplitude or another will contain some minimum level of error due to quantum uncertainty. This provides an example where quantum mechanics manifests itself in mainstream optical applications, such as telecommunications with an intensity or phase-modulated laser source. Quantum mechanics introduces a minimum level of error in any such communication system. I will discuss the fundamental nature of this uncertainty and describe the optimal quantum measurement that one would want to perform to minimize quantum uncertainty. I will then describe experimental results in which we utilized techniques from real-time feedback control on the quantum state of the light to achieve the minimum error allowed by nature for distinguishing between two distinct optical coherent states.

Tuesday, September 4th, at 3:00 pm

Department of Physics and Astronomy, Room 190

Refreshments will be served at the talk.