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arXiv:quant-ph/0502177 · Quantum Information and Computation

Precise creation, characterization, and manipulation of single optical qubits

Nicholas A. Peters, Joseph B. Altepeter, Evan R. Jeffrey, David A. Branning, Paul G. Kwiat

Published Oct 1, 2003• 25 citations
arXivHTMLPDF

Abstract

We present the theoretical basis for and experimental verification of arbitrary single-qubit state generation, using the polarization of photons generated via spontaneous parametric downconversion. Our precision measurement and state reconstruction system has the capability to distinguish over 3 million states, all of which can be reproducibly generated using our state creation apparatus. In order to complete the triumvirate of single qubit control, there must be a way to not only manipulate single qubits after creation and before measurement, but a way to characterize the manipulations themselves. We present a general representation of arbitrary processes, and experimental techniques for generating a variety of single qubit manipulations, including unitary, decohering, and (partially) polarizing operations.

DOI
10.26421/qic3.s-4

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We present the theoretical basis for and experimental verification of arbitrary single-qubit state generation, using the polarization of photons generated via spontaneous parametric downconversion. Our precision measurement and state reconstruction system has the capability to distinguish over 3 million states, all of which can be reproducibly generated using our state creation apparatus. In order to complete the triumvirate of single qubit control, there must be a way to not only manipulate single qubits after creation and before measurement, but a way to characterize the manipulations themselves. We present a general representation of arbitrary processes, and experimental techniques for generating a variety of single qubit manipulations, including unitary, decohering, and (partially) polarizing operations.
Using a spontaneous parametric-downconversion source of photon pairs, we are working towards the creation of arbitrary 2-qubit quantum states with high fidelity. Currently, all physically allowable combinations of polarization entanglement and mixture can be produced, including maximally-entangled mixed states. The states are experimentally measured and refined via computer-automated quantum-state tomography, and this system has also been used to perform single-qubit and ancilla-assisted quantum process tomography.
We present an experimentally feasible scheme to create single photons deterministically out of a non-deterministic spontaneous parametric downconversion source. We give an efficiency analysis of obtaining exactly one photon in the output. Furthermore, we experimentally demonstrate a way to control the purity of an output photon using a partial measurement of a polarization-entangled photon pair, a partial implementation of remote state preparation. When combined, these two techniques could allow on-demand preparation of single photons in arbitrary states.
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Summary form only given. Entangled states are increasingly important for a number of emergent quantum technologies, including cryptography, teleportation, and computation. In order to fully exploit the potential of these technologies, the ability to create, manipulate and characterize arbitrary quantum states is vital. Here we present theoretical and experimental investigations on the production of general quantum states (e.g., partially mixed and partially entangled) of two qubits, represented by the polarization degrees of freedom of photons.