The Fourth Annual Canadian Quantum Information Students' Conference
We present an entanglement verification method for systems with underlying qubit-mode structure, which does not require full knowledge of the bi-partite density matrix. It is applied to a quantum key distribution experiment with coherent signal states and one of two different detection schemes: For heterodyne detection, it is possible to detect entanglement even in the presence of loss and noise whereas for Stokes operator measurements, entanglement verification fails.
We present an information-theoretically secure protocol for the
transmission of a quantum state between an anonymous sender and an
anonymous receiver. The anonymity is perfect and so is the privacy
of the message. No assumption is made on the number of honest
participants and this leads to a protocol in which a single participant can cause an abort. Unless the receiver is corrupt, the quantum state is never destroyed; thus the state is either transferred to the receiver or it remains in the hands of the sender.
For most variations of Quantum finite automata (QFA), it is an open question to characterize the language recognition power of these machines. We extend several techniques used to obtain lower bounds on Kondacs and Watrous' 1-way Quantum Finite Automata to the case of Nayak's Generalized Quantum Finite Automata (GQFA). A consequence of these results is that the class of languages recognized by GQFAs is not closed under union.
A new source of polarization entangled photons is presented based on a bidirectionally pumped spontaneous parametric down-conversion crystal in the loop of a Sagnac interferometer. The source is pumped with a pulsed Ti:SA laser, allowing for high photon pair production rates and the potential for multi-photon experiments. Implementation, detection, and preliminary experimental results will be discussed.
Almost all known superpolynomial quantum speedups over classical algorithms have used the quantum Fourier transform (QFT). Most known applications of the QFT make use of the QFT over abelian groups, including Shor’s well known factoring algorithm [1]. However, the QFT can be generalised to act on non-abelian groups allowing different applications. For example, Kuperberg solves the dihedral hidden subgroup problem in subexponential time using the QFT on the dihedral group. The aim of this research is to construct an efficient QFT on SU(2).
An approximate quantum encryption scheme uses a private key to encrypt a quantum state while leaking only a very small (though non-zero) amount of information to the adversary. Previous work has shown that while we need 2n bits of key to encrypt n qubits exactly, we can get away with only n bits in the approximate case, provided that we know that the state to be encrypted is not entangled with something that the adversary already has in his possession.