Compact 6 dB Two-Color Continuous Variable Entangled Source Based on a Single Ring Optical Resonator

Abstract

Continuous-variable entangled optical beams at the degenerate wavelength of 0.8 µm or 1.5 µm have been investigated extensively, but separately. The two-color entangled states of these two useful wavelengths, with sufficiently high degrees of entanglement, still lag behind. In this work, we analyze the various limiting factors that affect the entanglement degree. On the basis of this, we successfully achieve 6 dB of two-color quadrature entangled light beams by improving the escape efficiency of the nondegenerate optical amplifier, the stability of the phase-locking servo system, and the detection efficiency. Our entangled source is constructed only from a single ring optical resonator, and thus is highly compact, which is suitable for applications in long-distance quantum communication networks.

Two-colour high-purity Einstein-Podolsky-Rosen photonic state

“…For a Gaussian state with the covariance matrix , assuming no phase-amplitude correlations between different modes 38 , the state purity is given by which yields μ = 0.63 ± 0.16. Our results compare favorably with the highest to date two-colour entanglement with purity 0.11 (corrected by the reported ) observed in the MHz range 22 . High purity is especially relevant for quantum enhancement of interferometry where both quadratures can contain useful information 39 , 40 .…”

“…The non-degenerate parametric process produces nonclassical correlation via annihilation of a photon with the frequency ω 0 (pump) generating twin photons pairs with frequencies ω 1 (signal) and ω 2 (idler); satisfying ω 0 = ω 1 + ω 2 and having the squeezed state production as the degenerate case where ω 1 = ω 2 . Previous approaches to generation of multi-colour CV quantum correlations with frequency non-degenerate optical parametric oscillators (NOPO) utilized operation above the oscillation threshold and resulted in modest levels of entanglement 20 – 22 . Noteworthy, to the best of our knowledge, low-frequency (<500 kHz) two-colour entanglement relevant for sensing applications has never been demonstrated.…”

Two-Color Quantum Correlation between Down-Conversion Beams at 1.5 and 3.3 μm from a Singly Resonant Optical Parametric Oscillator

“…As a matter of fact, the optical entangled state with different frequencies, which is an essential quantum source for constructing continuous variable (CV) quantum information networks and establishing connections between systems with different natures, consists of two sub-modes with quantum correlation at different frequencies between the quadrature amplitudes and between the quadrature phases [13][14][15]. In recent years, two-color, even three-color quantum correlations between signal-idler or pump-signal-idler beams were demonstrated using a non-degenerate optical parametric oscillator (NOPO) with doubly or triply resonant configurations [13][14][15][16][17]. The two-color quantum correlated beams at 0.8 and 1.5 µm can be utilized directly to make a connection between a quantum memory device based on alkaline atoms and a quantum communication device based on telecommunication optical fibers [16,17].…”

“…In recent years, two-color, even three-color quantum correlations between signal-idler or pump-signal-idler beams were demonstrated using a non-degenerate optical parametric oscillator (NOPO) with doubly or triply resonant configurations [13][14][15][16][17]. The two-color quantum correlated beams at 0.8 and 1.5 µm can be utilized directly to make a connection between a quantum memory device based on alkaline atoms and a quantum communication device based on telecommunication optical fibers [16,17]. In addition, the quantum-correlated twin beams had been successfully employed to improve the sensitivity beyond the SNL for signal recovery, absorption measurement, two-photon absorption spectroscopy, and realize the sub-shot-noise imaging of weak absorbing objects [18][19][20][21][22][23][24].…”

“…The two-color quantum correlation between twin beams was usually obtained using NOPO with doubly or triply resonant configurations [13][14][15][16][17]. However, stable operation and frequency tuning continuously without mode hopping are difficult to achieve using doubly or triply resonant NOPOs because simultaneous cavity resonance conditions should be fulfilled.…”