It is well known that photon antibunching may be obtained in strongly coupled single atom-photon systems in an optical cavity. The strong nonlinearities that come up in such configuration may be used to realize single photon optical switches [englund07][volz12] that ensure one photon transmission when the cavity is illuminated with a coherent state. Such a mechanism is called photon blockade [imamoglu97][birnbaum05], and it constitutes one of the conventional routes to generate single photons [faraon08]. Coupling a single atom (real or artificial) to a cavity suffers from severe technical issues that usually prevent room temperature operation, scalability, integration on a CMOS platform, among others.
Recently, a novel approach has been theoretically proposed to achieve single photon emission: the “Unconventional Photon Blockade” (UPB) mechanism, first proposed by V. Savona et al. [liew11]. Unlike conventional blockade based on strong one-photon nonlinearities, UPB only needs coupled cavities in presence of weak nonlinearities. It is the combination of the resulting nonlinear phase shifts and the two-cavity destructive interference which gives rise to photon antibunching. The interplay between slight nonlinear energy shifts and photon tunneling between the cavities leads to quantum interference, hence the suppression of multi-photon states. The theoretical explanation of such mechanisms has been proposed by the MPQ partner [bamba11].
The C2N partner [hamel15] has recently demonstrated the spontaneous symmetry breaking and flip-flop switching of photonic states in coupled photonic crystal nanolasers. The strong third order nonlinearities occurring in quantum well (QW) media were able to block photon tunneling between the nanolasers, which resulted in photon localization. This has been shown to occur with only 100 photons in the cavities, opening new exciting avenues for the investigation of quantum correlations with few photons. A preliminary theoretical study by the MPQ group has revealed strong quantum effects in the spontaneous symmetry breaking process even with a number of photons of the order of a few tens. In particular, correlations between photons emitted from different cavities are predicted to be enhanced close to the bifurcation points.
The intracavity photon number leading to SSB in the active regime scales with [hamel15]: i) the intercavity coupling strength; ii) the nanolaser saturation photon number. Using the potential barrier engineering technique developed by the C2N partner, the former may reduce the photon number at the onset of SSB by a factor ~3, which is eventually limited by fabrication tolerance. The latter, in turn, scales with the inverse of the spontaneous emission factor of the nanolasers. Typical beta-factors in Ref [hamel15] were ~0.02, and they can be improved by more than one order of magnitude by means of the photonic crystal geometry design [takiguchi16]. Combining i) and ii), the photon number at SSB transition can be scaled down to less than 10 photons, and hence few photon quantum correlations can be expected. Contrary to UPB, which evolves in a theory-to-experiment direction, SSB in the quantum regime has followed the way back, as it has been initially motivated by the recent experimental demonstration in the “mesoscopic” (hundreds photons) regime.
MPQ partner has recently theoretically discovered universal scaling laws in the hysteresis cycles of few photon bistable cavities. Quantum fingerprints of bistable transitions are thus predicted to appear in some physical observables such as 2-photon correlations [g(2)]. LKB partner has a well-established expertise in the investigation and measurement of the polariton optical bistability and of the related quadrature squeezing in semiconductor systems in the continuous variable regime. After the first observation of the optical bistability in a planar semiconductor microcavity [baas04], LKB partner has observed significant intensity squeezing (40% below the shot noise level) in semiconductor micro-pillars in strong coupling regime, by exploiting the effective polariton Kerr-like nonlinearities, enhanced by the confined geometry [boulier14]. The proposed experimental platforms of the project UNIQ will provide a unique opportunity to explore this new regime of bistability where quantum fluctuations play a dominant role.
[englund07] D. Englund, A. Faraon, I. Fushman, N. Stoltz, P. Petroff, J. Vučković, "Controlling cavity reflectivity with a single quantum dot", Nature 450, 857 (2007)
[volz12] T. Volz, A. Reinhard, M. Winger, A. Badolato, K. J. Hennessy, E. L. Hu and A. Imamoglu, "Ultrafast all-optical switching by single photons", Nature Photonics 6, 605 (2012)
[imamoglu97] A. Imamoḡlu, H. Schmidt, G. Woods, and M. Deutsch, “Strongly Interacting Photons in a Nonlinear Cavity”, Phys. Rev. Lett. 79, 1467 (1997)
[birnbaum05] K. M. Birnbaum, A. Boca, R. Miller, A. D. Boozer, T. E. Northup and H. J. Kimble, "Photon blockade in an optical cavity with one trapped atom", Nature 436, 87–90 (2005).
[faraon08] A. Faraon, I. Fushman, D. Englund, N. Stoltz, P. Petroff, J. Vuckovic, "Coherent generation of nonclassical light on a chip via photon-induced tunneling and blockade", Nature Phys. 4, 859 (2008)
[liew11] T. C. H. Liew, and V. Savona "Single photons from coupled quantum modes", PRL 104, 183601 (2010)
[bamba11] M. Bamba, A. Imamoğlu, I. Carusotto, C. Ciuti, "Origin of strong photon antibunching in weakly nonlinear photonic molecules", Physical Review A 83, 021802 (2011)
[hamel15] P. Hamel, S. Haddadi, F. Raineri, (…), J. A. Levenson and A. M. Yacomotti, "Spontaneous mirror-symmetry breaking in coupled photonic-crystal nanolasers", Nature Photonics 9, 311 (2015).
[takiguchi16] M. Takiguchi, …, and M. Notomi, "Systematic study of thresholdless oscillation in high-β buried multiple-quantum-well photonic crystal nanocavity lasers," Opt. Express 24, 3441 (2016).
[baas04] A. Baas, J.-Ph.Karr, M. Romanelli, A. Bramati, E. Giacobino, "Optical bistability in semiconductor microcavities in the nondegenerate parametric oscillation regime: analogy with the optical parametric oscillator ", Phys. Rev. B 70, 161307(R) (2004)
[boulier14] T. Boulier, M. Bamba, A. Amo, C. Adrados, A. Lemaitre, E. Galopin, I. Sagnes, J. Bloch, C. Ciuti, E. Giacobino and A. Bramati, "Polariton-generated intensity Squeezing in semiconductor micropillars" Nature Communications 5, doi:10.1038/ncomms4260 (2014)