Fiber coupled EPR-state generation from a single squeezing source

Using the continuous variable regime of light for measurement based quantum computation has shown advantages, as a large number of gates are readily available, and the resource cluster-state can be deterministically generated.... [ view full abstract ]

Using the continuous variable regime of light for measurement based quantum computation has shown advantages, as a large number of gates are readily available, and the resource cluster-state can be deterministically generated. With temporal encoding, the computation is scalable in time, and optical switching and delay becomes important. In this work a fast optical switch and 200m fiber is used to generate entangled EPR-states from a single squeezing source as sketched in figure 1 – a proof of concept in using switches and delay lines in quantum optical circuits. Furthermore, the EPR-state is generated in fiber at telecom wavelength, and thus straightforward to use in an optical fiber network for fiber coupled cluster-state generation and computation.

Squeezed vacuum states are generated in a free space optical parametric oscillator (OPO), and coupled into fiber with a 97% efficiency. Here a fast fiber switch alternately guides the squeezed light of two different temporal modes into a direct and a 200m delayed fiber path. After the delay the two modes overlap in time, and are then spatially overlapped in a fiber coupler generating an in-fiber EPR-state. Finally, the EPR-state is characterized by fiber based homodyne detection in each mode.

Figure 2 shows the measured two-mode squeezing of the EPR-state in the spectrum of the OPO. In the current state of the setup, we measure 3.5dB squeezing. The propagation efficiency through all fiber components is 80%, and the limiting factor is accuracy of phase locks. To improve on this, we are developing an efficient fiber based phase controller.

In conclusion, fiber coupled EPR-states has successfully been generated from a single squeezing source, and the experiment works as a proof of concept in using optical switching and delay in temporal encoded quantum optics. Towards this demonstration, we have developed several fiber-based technologies to be used in future CV quantum information processing schemes.