46 research outputs found
Geometrically-controlled polarisation processing in an integrated photonic platform
The polarisation of light is a powerful and widely used degree of freedom to
encode information, both in classical and quantum applications. In particular,
quantum information technologies based on photons are being revolutionised by
the use of integrated photonic circuits. It is therefore very important to be
able to manipulate the polarisation of photons in such circuits. We
experimentally demonstrate the fabrication by femtosecond laser micromachining
of components such as polarisation insensitive or polarising directional
couplers, operating at 1550 nm wavelength, where the two opposite behaviours
are achieved just by controlling the geometric layout of the photonic circuits,
being the waveguides fabricated with the same irradiation recipe. We expect to
employ this approach in complex integrated photonic devices, capable of a full
control of the photons polarisation for quantum cryptography, quantum
computation and quantum teleportation experiments.Comment: 9 pages, 7 figure
Fractional Bloch oscillations in photonic lattices
Bloch oscillations, the oscillatory motion of a quantum particle in a
periodic potential, are one of the most fascinating effects of coherent quantum
transport. Originally studied in the context of electrons in crystals, Bloch
oscillations manifest the wave nature of matter and are found in a wide variety
of different physical systems. Here we report on the first experimental
observation of fractional Bloch oscillations, using a photonic lattice as a
model system of a two-particle extended Bose-Hubbard Hamiltonian. In our
photonic simulator, the dynamics of two correlated particles hopping on a
one-dimensional lattice is mapped into the motion of a single particle in a
two-dimensional lattice with engineered defects and mimicked by light transport
in a square waveguide lattice with a bent axis
Symmetric polarization insensitive directional couplers fabricated by femtosecond laser waveguide writing
We study analytically the polarization behaviour of directional couplers
composed of birefringent waveguides, showing that they can induce polarization
transformations that depend on the specific input-output path considered. On
the basis of this study, we propose and demonstrate experimentally, by
femtosecond laser writing, directional couplers that are free from this problem
and also yield a polarization independent power-splitting ratio. More in
detail, we devise two different approaches to realize such devices: the first
one is based on local birefringence engineering, while the second one exploits
ultra-low birefringence waveguides obtained by thermal annealing
Quantum frequency conversion of quantum memory compatible photons to telecommunication wavelengths
We report an experiment demonstrating quantum frequency conversion of weak
light pulses compatible with atomic quantum memories to telecommunication
wavelengths. We use a PPLN nonlinear waveguide to convert weak coherent states
at the single photon level with a duration of 30ns from a wavelength of 780nm
to 1552nm. We measure a maximal waveguide internal (external) conversion
efficiency eta_int = 0.41 (eta_ext = 0.25), and we show that the signal to
noise ratio (SNR) is good enough to reduce the input photon number below 1. In
addition, we show that the noise generated by the pump beam in the crystal is
proportional to the spectral bandwidth of the device, suggesting that narrower
filtering could significantly increase the SNR. Finally, we demonstrate that
the quantum frequency converter can operate in the quantum regime by converting
a time-bin qubit and measuring the qubit fidelity after conversion.Comment: 15 pages, 5 figures (To appear in Optics Express
Integrated optical waveplates for arbitrary operations on polarization-encoded single-qubits
Integrated photonic technologies applied to quantum optics have recently
enabled a wealth of breakthrough experiments in several quantum information
areas. Path encoding was initially used to demonstrate operations on single or
multiple qubits. However, a polarization encoding approach is often simpler and
more effective. Two-qubits integrated logic gates as well as complex
interferometric structures have been successfully demonstrated exploiting
polarization encoding in femtosecond-laser-written photonic circuits. Still,
integrated devices performing single-qubit rotations are missing. Here we
demonstrate waveguide-based waveplates, fabricated by femtosecond laser pulses,
capable to effectively produce arbitrary single-qubit operations in the
polarization encoding. By exploiting these novel components we fabricate and
test a compact device for the quantum state tomography of two
polarization-entangled photons. The integrated optical waveplates complete the
toolbox required for a full manipulation of polarization-encoded qubits
on-chip, disclosing new scenarios for integrated quantum computation, sensing
and simulation, and possibly finding application also in standard photonic
devices
Experimental multiphase estimation on a chip
Multiparameter estimation is a general problem that aims at measuring unknown
physical quantities, obtaining high precision in the process. In this context,
the adoption of quantum resources promises a substantial boost in the
achievable performances with respect to the classical case. However, several
open problems remain to be addressed in the multiparameter scenario. A crucial
requirement is the identification of suitable platforms to develop and
experimentally test novel efficient methodologies that can be employed in this
general framework. We report the experimental implementation of a
reconfigurable integrated multimode interferometer designed for the
simultaneous estimation of two optical phases. We verify the high-fidelity
operation of the implemented device, and demonstrate quantum-enhanced
performances in two-phase estimation with respect to the best classical case,
post-selected to the number of detected coincidences. This device can be
employed to test general adaptive multiphase protocols due to its high
reconfigurability level, and represents a powerful platform to investigate the
multiparameter estimation scenario.Comment: 10+7 pages, 7+4 figure
Path-polarization hyperentangled and cluster states of photons on a chip
Encoding many qubits in different degrees of freedom (DOFs) of single photons
is one of the routes towards enlarging the Hilbert space spanned by a photonic
quantum state. Hyperentangled photon states (i.e. states showing entanglement
in multiple DOFs) have demonstrated significant implications for both
fundamental physics tests and quantum communication and computation. Increasing
the number of qubits of photonic experiments requires miniaturization and
integration of the basic elements and functions to guarantee the set-up
stability. This motivates the development of technologies allowing the precise
control of different photonic DOFs on a chip. We demonstrate the contextual use
of path and polarization qubits propagating within an integrated quantum
circuit. We tested the properties of four-qubit linear cluster states built on
both DOFs. Our results pave the way towards the full integration on a chip of
hybrid multiqubit multiphoton states.Comment: 7 pages, 7 figures, RevTex4-1, Light: Science & Applications
AAP:http://aap.nature-lsa.cn:8080/cms/accessory/files/AAP-lsa201664.pd
Dynamic band collapse in photonic graphene
The band structure and the transport properties of graphene are known to be deeply modified by strong electromagnetic fields. Here we experimentally demonstrate, using an engineered optical waveguide lattice as a model system for ac-driven graphene, the partial and complete collapse of valence and conduction quasi-energy bands corresponding to linearly- and circularly-polarized monochromatic light irradiation, respectively
Experimental Perfect Quantum State Transfer
The transfer of data is a fundamental task in information systems.
Microprocessors contain dedicated data buses that transmit bits across
different locations and implement sophisticated routing protocols. Transferring
quantum information with high fidelity is a challenging task, due to the
intrinsic fragility of quantum states. We report on the implementation of the
perfect state transfer protocol applied to a photonic qubit entangled with
another qubit at a different location. On a single device we perform three
routing procedures on entangled states with an average fidelity of 97.1%. Our
protocol extends the regular perfect state transfer by maintaining quantum
information encoded in the polarisation state of the photonic qubit. Our
results demonstrate the key principle of perfect state transfer, opening a
route toward data transfer for quantum computing systems