The precise quantum control of single photons, together with the intrinsic advantage of being mobile make optical quantum system ideally suited for delegated quantum information tasks, reaching from well-established quantum cryptography to quantum clouds and quantum computer networks.
Here I will present that the exploit of quantum photonics allows for a variety of quantum-enhanced data security for quantum and classical computers. First, I will present a homomorphic-encrypted quantum random walk using single-photon states and non-birefringent integrated optics. The client encrypts their input state in the photons’ polarization degree of freedom, while the server performs the computation using the path degree of freedom. Then I will briefly discuss the realization of a feasible hybrid classical-quantum technology, which shows promising new applications of readily available quantum photonics technology for secure classical computing by enabling probabilistic one-time programs.
In the emerging field of quantum information technology the two basic subfields are quantum communication
and quantum computation. Photonic qubits are considered as most promising information carriers for this
new technology due to the immense advantage of suffering negligible decoherence. Additionally, the very small
photon-photon interactions can be replaced by inducing effective nonlinearities via measurements which allow for
the implementation of crucial two-qubit gate operations. Although the spontaneous parametric down-conversion
gives access to the generation of highly entangled few-photon states, such as four-qubit cluster states which
allow to demonstrate the new concept of the one-way quantum computer, its applicability is highly limited
due to the poor scaling of the simultaneous emission of more than one-entangled photon pair. Therefore of
particular interest is the reversible mapping of qubits from photon states to atomic states. This might allow
the implementation of photonic quantum repeaters for long-distance quantum communication or the generation
of arbitrary multi-photon states as required for linear-optics quantum computing. Thus for the realization of
such a quantum network several approaches for achieving the required quantum control between matter and
photons have been studied during the past few years. Recent experiments demonstrating the generation of
narrow-bandwidth single photons using a room-temperature ensemble of <sup>87</sup>Rb atoms and electromagnetically
induced transparency should emphasize the progress towards such a quantum network.
Quantum metrology utilizes nonclassical states (of light) to
outperform the accuracy limits of its classical counterpart. We
demonstrate the relevance of photon number Fock states and
polarization entanglement for the experimental realization of
interferometric quantum metrology applications.