Jonathan Lavoie

Spectral compression of single photons

Researchers demonstrate bandwidth compression of single photons from 1740 GHz to 43 GHz, and tuning the center wavelength from 379 nm to 402 nm. The scheme relies on sum-frequency generation with frequency-chirped laser pulses. This technique enables interfacing between different quantum systems whose absorption and emission spectral properties are mismatched.

Quantum-inspired interferometry with chirped laser pulses

The precision of various interferometric measurements can be enhanced by using entangled states of light. Now an experiment demonstrates that all the metrological advantages of the famed Hong–Ou–Mandel quantum interferometer can be realized even with purely classical light.

Experimental bound entanglement in a four-photon state.

Bound entanglement is central to many exciting theoretical results in quantum information processing, but has thus far not been experimentally realized. In this work, we consider a one-parameter family of four-qubit Smolin states. We experimentally produce these states in the polarization of four optical photons produced from parametric down-conversion. Within a range of the parameter, we show that our states are entangled and undistillable, and thus bound entangled. Using these bound-entangled states we demonstrate entanglement unlocking.

Experimental violation of Svetlichny's inequality

It is well known that quantum mechanics is incompatible with local realistic theories. Svetlichny showed, through the development of a Bell-like inequality, that quantum mechanics is also incompatible with a restricted class of nonlocal realistic theories for three particles where any two-body nonlocal correlations are allowed (Svetlichny 1987 Phys. Rev. D 35 3066). In the present work, we experimentally generate three-photon GHZ states to test Svetlichnys inequality. Our states are fully characterized by quantum state tomography using an overcomplete set of measurements and have a fidelity of (84±1)% with the target state. We measure a convincing, 3.6σ, violation of Svetlichnys inequality and rule out this class of restricted nonlocal realistic models.

Quantum-optical coherence tomography with classical light.

Quantum-optical coherence tomography (Q-OCT) is an interferometric technique for axial imaging offering several advantages over conventional methods. Chirped-pulse interferometry (CPI) was recently demonstrated to exhibit all of the benefits of the quantum interferometer upon which Q-OCT is based. Here we use CPI to measure axial interferograms to profile a sample accruing the important benefits of Q-OCT, including automatic dispersion cancellation, but with 10 million times higher signal. Our technique solves the artifact problem in Q-OCT and highlights the power of classical correlation in optical imaging.

Optical one-way quantum computing with a simulated valence-bond solid

One-way quantum computing requires an entangled multiqubit system. So-called cluster states have been proposed to provide this resource, but they are difficult to generate. An alternative that uses the ground state of a one-dimensional chain of spins is now experimentally realized and used to construct a quantum logic gate.

Experimental three-photon quantum nonlocality under strict locality conditions

Violation of the classical bound of the three-particle Mermin inequality by nine standard deviations is experimentally demonstrated by closing both the locality and freedom-of-choice loopholes; only the fair-sampling assumption is required. To achieve this, a light source for producing entangled multiphoton states and measurement technologies for precise timing and efficient detection were developed.

Classical analogues of two-photon quantum interference.

Chirped-pulse interferometry (CPI) captures the metrological advantages of quantum Hong-Ou-Mandel (HOM) interferometry in a completely classical system. Modified HOM interferometers are the basis for a number of seminal quantum-interference effects. Here, the corresponding modifications to CPI allow for the first observation of classical analogues to the HOM peak and quantum beating. They also allow a new classical technique for generating phase super-resolution exhibiting a coherence length dramatically longer than that of the laser light, analogous to increased two-photon coherence lengths in entangled states.

Coherent ultrafast measurement of time-bin encoded photons.

Time-bin encoding is a robust form of optical quantum information, especially for transmission in optical fibers. To readout the information, the separation of the time bins must be larger than the detector time resolution, typically on the order of nanoseconds for photon counters. In the present work, we demonstrate a technique using a nonlinear interaction between chirped entangled time-bin photons and shaped laser pulses to perform projective measurements on arbitrary time-bin states with picosecond-scale separations. We demonstrate a tomographically complete set of time-bin qubit projective measurements and show the fidelity of operations is sufficiently high to violate the Clauser-Horne-Shimony-Holt-Bell inequality by more than 6 standard deviations.

Storage of hyperentanglement in a solid-state quantum memory

Two photons can simultaneously share entanglement between several degrees of freedom such as polarization, energy-time, spatial mode, and orbital angular momentum. This resource is known as hyperentanglement, and it has been shown to be an important tool for optical quantum information processing. Here we demonstrate the quantum storage and retrieval of photonic hyperentanglement in a solid-state quantum memory. A pair of photons entangled in polarization and energy-time is generated such that one photon is stored in the quantum memory, while the other photon has a telecommunication wavelength suitable for transmission in optical fiber. We measured violations of a Clauser–Horne–Shimony–Holt Bell inequality for each degree of freedom, independently of the other one, which proves the successful storage and retrieval of the two bits of entanglement shared by the photons. Our scheme is compatible with long-distance quantum communication in optical fiber, and is in particular suitable for linear-optical entanglement purification for quantum repeaters.