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
