Strongly interacting photons in hollow-core waveguides

Abstract

Hollow-core photonic-crystal waveguides filled with cold atoms can support giant optical nonlinearities through nondispersive propagation of light tightly confined in the transverse direction. Here we explore electromagnetically induced transparency is such structures, considering a pair of counter-propagating weak quantum fields in the medium of coherently driven atoms in the ladder configuration. Strong dipole--dipole interactions between optically excited, polarized Rydberg states of the atoms translate into a large dispersive interaction between the two fields. This can be used to attain a spatially-homogeneous conditional phase shift of pi for two single-photon pulses, realizing a deterministic photonic phase gate, or to implement a quantum nondemolition measurement of the photon number in the signal pulse by a coherent probe, thereby achieving a heralded source of single or few photon pulses

Quantum nonlinear optics with single photons enabled by strongly interacting atoms

“…The quantum nonlinearity is obtained by coherently coupling slowly propagating photons [3][4][5] to strongly interacting atomic Rydberg states [6][7][8][9][10][11][12] in a cold, dense atomic gas 13 . Our approach opens the door for quantum-byquantum control of light fields, including single-photon switching 14 , all-optical deterministic 1 quantum logic 15 , and the realization of strongly correlated many-body states of light 16 .Recently, remarkable advances have been made towards optical systems that are nonlinear at the level of individual photons. The most promising approaches have used high-finesse optical cavities to enhance the atom-photon interaction probability 2,[17][18][19][20][21] .…”

“…The quantum nonlinearity is obtained by coherently coupling slowly propagating photons [3][4][5] to strongly interacting atomic Rydberg states [6][7][8][9][10][11][12] in a cold, dense atomic gas 13 . Our approach opens the door for quantum-byquantum control of light fields, including single-photon switching 14 , all-optical deterministic 1 quantum logic 15 , and the realization of strongly correlated many-body states of light 16 .…”

“…It can be used, e.g., for quantum non-demolition measurements of optical photons. At the same time, by using strong interactions in the dispersive regime, the present approach can be used to implement deterministic quantum logic gates 14,15 , which would constitute a major advance towards all-optical quantum information The probe beam is focused to a 1/e 2 waist w=4.5µm by a confocal arrangement of achro-matic doublet lenses with focal length 30mm and diameter 6.25mm. The control field is copropagating with the probe beam.…”

Photon-photon gate via the interaction between two collective Rydberg excitations

“…There is a significant body of work studying the effects of mapping photons onto collective atomic Rydberg excitations [14][15][16][17][18][19][20]. Most proposals for photon-photon gates involve propagating Rydberg excitations (polaritons), either using blockade [21,22] or two excitations [23][24][25][26].…”

“…Achieving blockade conditions can be challenging since both photons have to be localized within the blockade volume. Following [6,7,[23][24][25][26], we here propose a storage-based scheme that instead relies on the interaction between two stationary Rydberg excitations.The main challenge for two-excitation based Rydberg gates in atomic ensembles arises from the fact that the interaction is strongly distance-dependent and thus not uniform over the profiles of the two stored photons. We show that this a priori reduces the gate's fidelity by displacing the collective excitations in momentum space and by entangling their quantum states.…”