Marco Fiorentino

Generation of ultrabright tunable polarization entanglement without spatial, spectral, or temporal constraints

The need for spatial and spectral filtering in the generation of polarization entanglement is eliminated by combining two coherently driven type-II spontaneous parametric down-converters. The resulting ultrabright source emits photon pairs that are polarization entangled over the entire spatial cone and spectrum of emission. We detect a flux of ,12 000 polarization-entangled pairs/s per mW of pump power at 90% quantuminterference visibility, and the source can be temperature tuned for 5 nm around frequency degeneracy. The output state is actively controlled by precisely adjusting the relative phase of the two coherent pumps.

High-flux source of polarization-entangled photons from a periodically poled KTiOPO~4 parametric down-converter (5 pages)

We have demonstrated a high-flux source of polarization-entangled photons using a type-II phase-matched periodically poled KTiOPO{sub 4} parametric down-converter in a collinearly propagating configuration. We have observed quantum interference between the single-beam down-converted photons with a visibility of 99% together with a measured coincidence flux of 300 s{sup -1}/mW of pump. The Clauser-Horne-Shimony-Holt version of Bells inequality was violated with a value of 2.711{+-}0.017.

Deterministic Controlled-NOT Gate For Single-Photon Two-Qubit Quantum Logic

We demonstrate a robust implementation of a deterministic linear-optical controlled-not gate for single-photon two-qubit quantum logic. A polarization Sagnac interferometer with an embedded 45 degrees -oriented dove prism is used to enable the polarization control qubit to act on the momentum (spatial) target qubit of the same photon. The optical controlled-not gate requires no active stabilization because the two spatial modes share a common path, and it is used to entangle the polarization and momentum qubits.

Two-Photon Coincident-Frequency Entanglement via Extended Phase Matching

We demonstrate a new class of frequency-entangled states generated via spontaneous parametric down-conversion under extended phase-matching conditions. Biphoton entanglement with coincident signal and idler frequencies is observed over a broad bandwidth in periodically poled KTiOPO4. We demonstrate high visibility in Hong-Ou-Mandel interferometric measurements under pulsed pumping without spectral filtering, which indicates excellent frequency indistinguishability between the down-converted photons. The coincident-frequency entanglement source is useful for quantum information processing and quantum measurement applications.

Source of polarization entanglement in a single periodically poled KTiOPO4 crystal with overlapping emission cones.

We present a simple polarization entanglemenet source based on type-II phase-matched parametric down-conversion in periodically poled KTiOPO4. By use of noncritical phase matching in a noncollinear geometry the single-crystal source emits a cone of polarization-entangled photons. Two beams on opposite sides of the cone are selected for measurements to yield an observed flux of 820 pairs/s per mW of pump power with a two-photon fringe visibility of 96%. With this source we measure a violation of Bells inequality of 140 standard deviations in 160 s.

Single-photon two-qubit SWAP gate for entanglement manipulation

A SWAP operation between different types of qubits of single photons is essential for manipulating hyperentangled photons for a variety of applications. We have implemented an efficient SWAP gate for the momentum and polarization degrees of freedom of a single photon. The SWAP gate was utilized in a single-photon two-qubit quantum logic circuit to deterministically transfer momentum entanglement between a pair of down-converted photons to polarization entanglement. The polarization entanglement thus obtained violates Bells inequality by more than 150 standard deviations.

Ultrabright tunable photon-pair source with total-flux polarization-entanglement

We demonstrate a continuous-wave dual-pump tunable source of polarization-entangled photons that requires no spectral or spatial filtering and emits ten times more pairs per mW of pump than pervious sources.

Single‐Photon Two‐Qubit Logic Gates

We present experimental results of deterministic linear optical Controlled‐NOT and SWAP gates for single‐photon two‐qubit quantum logic. In our implementation one qubit is encoded in the polarization degree of freedom of the photon and the other is encoded in the momentum. Momentum‐ and polarization‐controlled NOT gates are demonstrated. They are then combined to form a SWAP gate to convert pairs of momentum‐entangled photons into polarization‐entangled photons.

Coincident-frequency entanglement via extended phase matching

We demonstrate a source of entangled photon pairs with identical frequency spectra. An Hong-Ou-Mandel interferometric measurement of this source shows a high visibility of 85% under pulsed pumping and without any spectral filtering.

Entanglement swapping in a single-photon two-qubit logic circuit

We have implemented a SWAP gate to transfer entanglement from the momentum to the polarization degree of freedom of down-converted photon pairs. The polarization-entangled pairs thus created violate Bells inequality by more than 150 standard deviations