Phys. Rev. A 85, 053824 (2012)

Quantum computing with light will likely require the use of exotic states such as 'optical Schrödinger's cats'. Unfortunately, such states are extreme fragile; they are highly susceptible to noise and rarely survive quantum teleportation, which is an important scheme for transferring quantum information. Shuntaro Takeda and co-workers from the University of Tokyo in Japan have now shown that an optical high-pass filter can remove the problematic low-frequency noise generated in most lasers, which usually destroys Schrödinger's cat states. A filter cavity in the trigger-photon channel removes unwanted noise from the spectrum where the quantum states are encoded. Unlike an electrical filter, which removes information from the measurement results, this optical high-pass filter preserves the original state. The researchers used this method to create high-quality Schrödinger's cat states of light and then tested their increased robustness in teleportation experiments. The teleported states had a central minimum of −0.033 in their Wigner functions, which indicates that these are the highest-quality cat states teleported to date.