Efficient microwave to optical photon conversion: an electro-optical realization

Abstract

Linking classical microwave electrical circuits to the optical telecommunication band is at the core of modern communication. Future quantum information networks will require coherent microwave-to-optical conversion to link electronic quantum processors and memories via low-loss optical telecommunication networks. Efficient conversion can be achieved with electro-optical modulators operating at the single microwave photon level. In the standard electro-optic modulation scheme, this is impossible because both up-and down-converted sidebands are necessarily present. Here, we demonstrate true single-sideband up-or down-conversion in a triply resonant whispering gallery mode resonator by explicitly addressing modes with asymmetric free spectral range. Compared to previous experiments, we show a 3 orders of magnitude improvement of the electro-optical conversion efficiency, reaching 0.1% photon number conversion for a 10 GHz microwave tone at 0.42 mW of optical pump power. The presented scheme is fully compatible with existing superconducting 3D circuit quantum electrodynamics technology and can be used for nonclassical state conversion and communication. Our conversion bandwidth is larger than 1 MHz and is not fundamentally limited.

Nonlinear and Quantum Optics with Whispering Gallery Resonators

“…However it may be efficient in the situations when the quasiequidistant character of the WGM spectrum needs to be altered, e.g. for the design of single sideband (SSB) electrooptical modulators(EOMs) [110]. Furthermore, in non-Hermitian systems where there is a loss for each mode, the avoided crossing near the degeneracy allows for realizing the so-called parity time symmetric (-Symmetric) systems [242][243][244], and even more generally, to study the exceptional points [238,[245][246][247].…”

“…The relative power of the first modulation sidebands is ( ) where n mw and n e are the extraordinary refractive indices at the microwave and optical frequencies, respectively, V mw is the microwave mode volume, r 33 is the electro-optical coefficient, and σ is thedimensionless overlap integral for the process. It is easy to verify that for a typical running wave modulator with = p V V 3 and  = 50 Ohm the saturation power exceeds 100mW, while for a lithium niobate WGM EOM with 10MHz bandwidth it is only about 2.5μW [110,298]. It means that the equivalent p V of such WGM EOM is less than 20mV.…”

Coherent Conversion Between Microwave and Optical Photons—An Overview of Physical Implementations

“…Light is prism‐coupled in and out of the WGMs. Reproduced with permission . Copyright 2016, OSA Publishing.…”

“…In ref. [], a LiNbO 3 disk was embedded in a solid copper cavity (Figure b), tuned to match the FSR = 8.9 GHz of the WGMs. The loaded microwave cavity had a quality of at room temperature, limited by ohmic losses; the carefully polished LiNbO 3 , however, showed a particularly high optical Q of ≈10 8 .…”

“…In order to reduce Stokes processes, the system in ref. [] was thermally tuned to an anticrossing between the bright TE modes and the dark TM modes . This resulted in sufficient asymmetry in the spacing of the adjacent WGMs that emission into the lower sideband was completely suppressed (Figure c).…”