# A CDE Definition

qubit

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**QU**antum

**BIT**) A unit of data in a quantum computer. The "bit" in qubit is somewhat misleading. Unlike a bit (binary digit) in a digital computer, which can hold a 0 or 1, a qubit can represent both a 0 and 1 at the same time or multiple states in between. In addition, the qubit is not a storage cell but typically an electron or photon, and the electron's charge or the photon's polarization determines the 0 or 1. See quantum computing.

quantum computing

A computer architecture based on quantum mechanics, the science of atomic structure and function. In 1999, the feasibility of such a computer was demonstrated by MIT, the University of California at Berkeley and Stanford University.

**Qubit Superposition and Entanglement**

The concept of quantum computing is that atoms can be made to perform high-level gating functions, and quantum devices are expected to achieve mathematical results 10,000 times faster than today's "classical" computers.

Quantum computing uses the "qubit," or quantum bit, comprising electrons or photons. Quantum superposition is the condition that allows a qubit to be in multiple states at the same time, not just a 0 or 1 (see qubit). Entanglement is the property that allows one particle to relate to another over distance.

**Molecular Modeling and Cryptography**

Today, quantum computers with only a handful of qubits are operating. However, when quantum computers with 100 or more qubits become viable, major breakthroughs are expected. For example, quantum phenomena govern how atoms interact, and it is believed that quantum computers may be able to model molecular activity and thus help develop genetic and pharmaceutical therapies.

New cryptographic algorithms could be developed that are unbreakable, and they would have to be invented because a quantum computer is expected to be able to decode today's cryptographic keys in seconds.

**A Lot Different Than Classical Computing**

Developing the quantum hardware is only one aspect. Just as difficult is coming up with algorithms that a quantum computer can actually use to solve problems. Merely adapting today's software to a quantum computer does not work and will often produce a slower result. There are still huge hurdles to overcome; for example, error correction is extremely difficult to implement. However, scientists believe everyday quantum computing is just a matter of time. See cryptography.

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