Abstract
Type II optical parametric oscillators are amongst the highest-quality sources of quantum-correlated light. In particular, when pumped above threshold, such devices generate a pair of bright orthogonally-polarized beams with strong continuous-variable entanglement. However, these sources are of limited practical use, because the entangled beams emerge with different frequencies and a diffusing phase difference. It has been proven that the use of an internal wave-plate coupling the modes with orthogonal polarization is capable of locking the frequencies of the emerging beams to half the pump frequency, as well as reducing the phase-difference diffusion, at the expense of reducing the entanglement levels. In this work we characterize theoretically an alternative locking mechanism: the injection of a laser at half the pump frequency. Apart from being less invasive, this method should allow for an easier real-time experimental control. We show that such an injection is capable of generating the desired phase locking between the emerging beams, while still allowing for large levels of entanglement. Moreover, we find an additional region of the parameter space (at relatively large injections) where a mode with well defined polarization is in a highly amplitude-squeezed state.
Highlights
Optical parametric oscillators (OPOs) are optical cavities containing a crystal with second order nonlinearity
Type I OPOs, in which both signal and idler are linearly polarized along the same direction, hold the record for quadrature noise reduction or single-mode squeezing (97% below vacuum fluctuations in [4], see [5,6,7,8,9] for previous experiments achieving more than 90% of noise reduction); this is manifested in the mode at the degenerate frequency w s = wi = w0, but squeezing is large only when working close to threshold [10]
As for the applications of this quantum-correlated light source, on one hand, squeezed light is a basic resource in the field of high-precission measurements, helping overcome the standard quantum limit imposed by vacuum fluctuations [11,12,13,14]
Summary
When pumped above threshold, such devices generate a pair of bright attribution to the author(s) and the title of orthogonally-polarized beams with strong continuous-variable entanglement. These the work, journal citation and DOI. It has been proven that the use of an internal wave-plate coupling the modes with orthogonal polarization is capable of locking the frequencies of the emerging beams to half the pump frequency, as well as reducing the phase-difference diffusion, at the expense of reducing the entanglement levels. Apart from being less invasive, this method should allow for an easier real-time experimental control We show that such an injection is capable of generating the desired phase locking between the emerging beams, while still allowing for large levels of entanglement.
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