Polarization Entangled State Measurement on a Chip

Abstract

The emerging strategy to overcome the limitations of bulk quantum optics consists of taking advantage of the robustness and compactness achievable by integrated waveguide technology. Here we report the realization of a directional coupler, fabricated by femtosecond laser waveguide writing, acting as an integrated beam splitter able to support polarization-encoded qubits. This maskless and single step technique allows us to realize circular transverse waveguide profiles which are able to support the propagation of gaussian modes with any polarization state. Using this device, we demonstrate quantum interference with polarization-entangled states and singlet state projection.

Temporal Purity and Quantum Interference of Single Photons from Two Independent Cold Atomic Ensembles

“…The traditional method to produce indistinguishable single photons is heralding time-frequency entangled biphotons generated from spontaneous parametric down-conversion (SPDC) in a nonlinear crystal which is pumped by ultrashort pulses [4,5,8]. In recent decades many new physical systems have been developed [9-13] to obtain pure single photons without time-frequency entanglement built in.In the community of quantum communication, SPDC in χ ð2Þ nonlinear media is still the preferable way to produce entangled biphotons because of its simplicity in the operation and the potential for on-chip integration and scaling up [14][15][16]. However, the intrinsic feasible phase matching condition of SPDC crystal allows an extremely broad range of temporal modes.…”

Deterministic separation of arbitrary photon pair states in integrated quantum circuits

“…Directional couplers have thus far been the most ubiquitous coupler type for implementing on-chip quantum interference [7][8][9][10][11]. When IFPS is implemented using such devices, its analysis has several key distinctions from the typical bulk-optics treatment.…”

“…While virtually all on-chip interference experiments [7][8][9][10][11]14] have been conducted near degeneracy, they have sampled only a small subset of the total parameter space (e.g. central wavelength separations, polarizations, photon bandwidths, coupler characteristics).…”

“…A variety of integrated couplers are available for mediating on-chip quantum interference, among which the directional coupler has been the most widely-used [7][8][9][10][11]. However, unlike the bulk-optics beamsplitters, the power splitting ratio of a directional and other integrated coupler types can have significant wavelength and polarization dependence.…”

“…Mapping quantum photonic technologies into an integrated on-chip setting has become an important task for overcoming the severe stability and scalability limitations of bulk-optics implementations. Recent efforts have demonstrated on-chip quantum state generation [4][5][6], manipulation [7][8][9][10][11][12] and detection [13] across numerous material platforms including GaAs [6,11,13], silicon wire [5,12], silica-on-silicon [7,8,10], lithium niobate [14] and borosilicate glass [9].…”