## Quantum Information Processing with Atoms and Photons

**Michael J. Jabines**

Quantum information science(QIS) is a new field of science and technology, combining and drawing on the disciplines of physical science, mathematics, computer science and engineering. Here, Quantum information processors exploit the quantum features of superposition and entanglement for application not possible in classical devices. It offers the potential for significant improvements in the communication and processing of information.

For an isolated quantum system, the fundamental unit of information is the quantum bit or qubit. Qubits are just quantum two-level system such as the spin of an electron or the polarization of a photon and can be prepared in a coherent superposition state. For a quantum information processor, there are three (3) requirements to have a good quantum hardware:

1. The quantum system must be initialized in a well-defined state.

2. Arbitrary unitary operators must be available and controlled to launch the initial state to an arbitrary entangled state.

3. Measurements of the qubits must be performed with high quantum efficiency.

The first requirements demand that the qubits are well isolated from the environment to ensure pure initial quantum states and to preserve their superposition character, but they must also interact strongly between one another to become entangled. Atomic gases and single photon are among promising candidates to implement quantum information technology because they can be well isolated from their environment. Despite this advantage it is challenging to design controllable interaction between these particles and to store or manipulate quantum information in a reliable way. Quantum information processing requires qubits to behave as quantum memories for long-storage and for many applications to behave as quantum transmitters for long-distance communication. Cold and localized individual atoms are the natural choice for qubit memories and sources of local entanglement for quantum information processing. Photons, on the other hand are the natural source for the communication of quantum information, as they can traverse large distance through the atmosphere or optical fibers with minimal distance.

Quantum information technology is likely to have an important role in information processing after the demise of Moore’s Law. Current devices come primarily from the areas of quantum optics and atomic physics, usually involving laser-cooled and trapped atoms. But perhaps the most exciting feature of this field is that the first-large scale quantum computer will probably be built from a physical system that is not currently known. Current experiments that control the individual atoms and photons will continue to lead the bizzare features of quantum-mechanical foundations to the forefront. With this new language of information, hope we can gain more insight in the underlying quantum-physical principle, exactly as Shannon’s theory of classical information ushered advance physics responsible for the current digital age.

*A summary of Christopher Monroe’s **“Quantum Information Processing with Atoms and Photons”**

**Michael Jabines** is a graduate student in Physics of Mindanao State University-Iligan Institute of technology (MSU-IIT) Iligan City Philippines.