Deterministic photon–emitter coupling in chiral photonic circuits

Abstract

The ability to engineer photon emission and photon scattering is at the heart of modern photonics applications ranging from light harvesting, through novel compact light sources, to quantuminformation processing based on single photons. Nanophotonic waveguides are particularly well suited for such applications since they confine photon propagation to a 1D geometry thereby increasing the interaction between light and matter. Adding chiral functionalities to nanophotonic waveguides lead to new opportunities enabling integrated and robust quantum-photonic devices or the observation of novel topological photonic states. In a regular waveguide, a quantum emitter radiates photons in either of two directions, and photon emission and absorption are reverse processes. This symmetry is violated in nanophotonic structures where a non-transversal local electric field implies that both photon emission [1,2] and scattering [3] may become directional. Here we experimentally demonstrate that the internal state of a quantum emitter determines the chirality of single-photon emission in a specially engineered photonic-crystal waveguide. Single-photon emission into the waveguide with a directionality of more than 90% is observed under conditions where practically all emitted photons are coupled to the waveguide. Such deterministic and highly directional photon emission enables on-chip optical diodes, circulators operating at the single-photon level, and deterministic quantum gates. Based on our experimental demonstration, we propose an experimentally achievable and fully scalable deterministic photon-photon CNOT gate, which so far has been missing in photonic quantum-information processing where most gates are probabilistic [4]. Chiral photonic circuits will enable dissipative preparation of entangled states of multiple emitters [5], may lead to novel topological photon states [6,7], or can be applied in a classical regime to obtain highly directional photon scattering [8][9][10].Truly 1D photon-emitter interfaces are desirable for a range of applications in photonic quantum-information processing [11]. To this end, photonic-crystal waveguides constitute an ideal platform featuring on-chip integration with the ability to engineer the light-matter coupling. Recent experiments have achieved a coupling efficiency for a single quantum dot (QD) to a photoniccrystal waveguide in excess of 98%, thus constituting a deterministic 1D photon-emitter interface [12]. Standard photonic-crystal waveguides are mirror symmetric around the center of the waveguide and as a consequence the mode polarization is predominantly linear at the positions where light intensity is high. By designing a photonic-crystal waveguide that breaks this symmetry, modes that are circularly polarized at the field maxima can be engineered. We refer to this novel type of waveguide as a glide-plane waveguide (GPW), cf. Supplementary Material for further descriptions of the structural parameters. In a GPW, a QD with a circularly polarized transition dipole emits preferential...

Chiral quantum optics

“…The associated directional coupling has been observed experimentally in both dielectric [21][22][23][24][25][26][27][28][29][30][31] and plasmonic nanostructures [32][33][34][35] by coupling both classical [24-26, 30, 32-35] and quantum [21-23, 27-29, 31] emitters to the confined light fields. The robustness of the chiral points against unavoidable fabrication imperfections in photonic-crystal waveguides has been assessed [31,36] and chiral coupling is a well characterized and robust phenomenon, which is readily implementable in a range of applications.…”

“…The considered radius of the fiber is 250 nm, wavelength 852 nm, refractive index 1.45, and the propagation direction is along +z. c Color map of the electric field intensity and local polarization of a photonic-crystal glide-plane waveguide [29]. The grey arrow shows the propagation direction and the inset shows the linear color scale from zero (dark colours) to maximum (light colours) scaled field intensity.…”

Interferometric quantum cascade systems

“…First interests in these models grew in the 80's because of the necessity of a formalism able to take into account the reaction of a quantum system (say an atom or a electromagnetic cavity) to the light emitted by another one [2][3][4][5][6][7][8]. In recent years there has been a revival of interest towards QCSs, due to the possibility of creating entangled states and other tasks for quantum computation [9][10][11][12], chiral optical networks [13][14][15], and in the managing of heat transmission [16]; also several experimental implementations have been proposed, exploiting, for instance, nanophotonic waveguides [17,18] and spin-orbit coupling [19].…”

Polarization Engineering in Photonic Crystal Waveguides for Spin-Photon Entanglers

“…However if one chooses to measure the phase of the forward propagating photon (e.g. with a Mach-Zehnder interferometer) then spin-path entanglement is a natural consequence [30]. This predicts a stark contrast between a charged QD at a C-point, where one always sees transmission, and a fine-structure split neutral QD where one always sees a reflection.…”