ИСТИНА

Under strong pumping, parametric down-conversion (PDC) leads to the generation of bright squeezed vacuum (BSV). This quantum state of light, although having a large (macroscopic) mean number of photons, still manifests nonclassical properties such as twin-beam squeezing [1] and polarization entanglement [2]. BSV, unless filtered in frequency and transverse wavevector, has highly multimode structure. On the one hand, this structure is useful for various applications such as quantum information encoding, quantum imaging, and quantum metrology. On the other hand, the presence of multiple modes makes it difficult to measure the quadrature squeezing of BSV. In this work [3] we solve this problem by applying to BSV the recently proposed technique of ‘optical homodyne’ [4]. In our experiment, spatially multimode BSV is produced through high-gain PDC and then focused into a second PDC source, so that in all angular/spatial modes, BSV is amplified or de-amplified depending on the phase introduced between the two sources. This configuration is known as the SU(1,1) interferometer. Among other applications, it provides the measurement of quadrature variance for the radiation emitted by the first source through the direct detection of the radiation at the output of the second source [4]. The measurement needs no external local oscillator (LO) and is tolerant to detection losses. By using this technique, we measure up to 4.3 dB quadrature squeezing and up to 15 dB anti-squeezing for various plane-wave modes of BSV with the mean photon number per mode up to 17. The possibility of loss-tolerant homodyne detection without an LO will simplify many quantum-information techniques, including one-way quantum computation. [1] O. Jedrkiewicz et al. PRL 93, 243601 (2004). [2] T.Sh. Iskhakov et al., PRL 109, 150502 (2012). [3] G. Frascella et al., arXiv:1905.03143v1 [quant-ph]. [4] Y. Shaked et al., Nature Communications 9, 609 (2018).