Homodyne measurement is a corner-stone of quantum optics. It measures the fundamental variables of quantum electrody namics - the quadratures of light\, which represent the cosine-wave and si ne-wave components of an optical field. The quadratures constitute the qua ntum optical analog of position and momentum in mechanics and obey quantum uncertainty\, indicating the inherent inability to measure both simultane ously. The homodyne process\, which extracts a chosen quadrature amplitude by correlating the optical field against an external quadrature reference (local-oscillator\, LO)\, forms the backbone of coherent detection in phy sics and engineering\, and plays a central role in quantum information pro cessing. Homodyne can reveal non-classical phenomena\, such as squeezing o f the quadrature uncertainty\; It is used in tomography to fully character ize quantum states of light\; Homodyne detection can generate non-classica l states\, provide local measurements for teleportation and serve as a maj or detector for quantum key distribution (QKD) and quantum computing. Yet\ , standard homodyne suffers from a severe bandwidth limitation. While the bandwidth of optical states can easily span many THz\, standard homodyne d etection is inherently limited to the electrically accessible\, MHz to GHz range\, leaving a dramatic gap between the relevant optical phenomena and the measurement capability. This gap impedes effective utilization of the huge bandwidth resource of optical states and the potential enhancement o f the information throughput \\emph{by several orders of magnitude} with p arallel processing in quantum computation\, QKD and other applications of quantum squeezed light. Here we demonstrate a fully parallel optical homod yne measurement across an arbitrary optical bandwidth\, effectively liftin g the bandwidth limitation completely. Using optical parametric amplificat ion\, which amplifies one quadrature while attenuating the other\, we meas ure two-mode quadrature squeezing of \;1.7dB below the vacuum level si multaneously across a bandwidth of \;55THz using a single LO - the pum p. This broadband parametric homodyne measurement opens a wide window for parallel processing of quantum information.

\n\n*Yaakobv
Shaked\, Yoad Michael\, Rafi Vered\, Leon Bello\, Michael Rosenbluh and&nb
sp\; Avi Pe'\;er\,*