This thesis describes a linear-optical device for performing generalized quantum measurements
on quantum bits (qubits) encoded in photon polarization, the implementation
of said device, and its use in two diff erent but related experiments. The device works by
coupling the polarization degree of freedom of a single photon to a `mode' or `path' degree
of freedom, and performing a projective measurement in this enlarged state space in order
to implement a tunable four-outcome positive operator-valued measure (POVM) on the
initial quantum bit. In both experiments, this POVM is performed on one photon from a
two-photon entangled state created through spontaneous parametric down-conversion.
In the fi rst experiment, this entangled state is viewed as a two-qubit photonic cluster
state, and the POVM as a means of increasing the computational power of a given resource
state in the cluster-state model of quantum computing. This model traditionally
achieves deterministic outputs to quantum computations via successive projective measurements,
along with classical feedforward to choose measurement bases, on qubits in a highly entangled
resource called a cluster state; we show that `virtual qubits' can be appended to a
given cluster by replacing some projective measurements with POVMs. Our experimental
demonstration fully realizes an arbitrary three-qubit cluster computation by implementing
the POVM, as well as fast active feed-forward, on our two-qubit photonic cluster state.
Over 206 diff erent computations, the average output delity is 0.9832 +/- 0.0002; furthermore
the error contribution from our POVM device and feedforward is only of order 10^-3, less
than some recent thresholds for fault-tolerant cluster computing.
In the second experiment, the POVM device is used to implement a deterministic
protocol for remote state preparation (RSP) of arbitrary photon polarization qubits. RSP
is the act of preparing a quantum state at a remote location without actually transmitting
the state itself. We are able to remotely prepare 178 diff erent pure and mixed qubit
states with an average delity of 0.995. Furthermore, we study the the fidelity achievable
by RSP protocols permitting only classical communication, without shared entanglement,
and compare the resulting benchmarks for average fidelity against our experimental results.
Our experimentally-achieved average fi delities surpass the classical thresholds whenever
classical communication alone does not trivially allow for perfect RSP.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OWTU.10012/4841 |
| Date | January 2009 |
| Creators | Biggerstaff, Devon |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation |
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