# Quantum Computing

# Quantum Computing and Information

From teleportation to spooky action-at-distance effects, the strange world of quantum mechanics can be anything from slightly puzzling to promising to fascinating. It is also an intricate toolbox that can be used to build the ultimate machine: the quantum computer. The quantum computer will make use of principles of quantum mechanics such as superposition and entanglement.

The basic unit of information, analogous to the classical bit, is called a qubit—literally, a quantum bit. However, while the classical bits can only be in a single state at a time, typically 0 or 1, qubits can be in a superposition of states. Different types of qubits are used to encode information, typically the vertical and horizontal polarization of light or the up and down spin of an electron. This superposition of qubits bestows the computer with intrinsic parallelism by allowing it to perform several operations simultaneously. Quantum computers are expected to be orders of magnitude faster and more powerful than the classical computer.

In addition, particles that exist in a superposition of states (photons, electrons, bosons) are entangled, i.e., their behavior and properties are strongly correlated, so much so that, despite being physically separated by rather large distances, any action on one particle will be reflected in the other. Entanglement can therefore be viewed as a measure of the integrity of the information that is being transmitted, and corrupted information can be automatically detected by simply “reading” the state of the system. Quantum computers are thus promising for data encryption and cryptanalysis. However, that same advantage is also an issue in the design and construction of a quantum computer. Entangled systems, if not properly isolated, will irreversibly interact with the environment, resulting in a “new” state. Thus, dephasing (or decoherence) occurs, and information is lost.

# At the Pittsburgh Quantum Institute

PQI researchers work on various aspects of quantum computing and information. Development in information theory as well as in quantum algorithms is carried out. Qubit platforms, such as superconducting microwave circuits and Majorana Fermions in semiconducting nanowires are designed for quantum computing. Quantum simulation is another approach to quantum computing; the experimental thrust is the design of a 1D solid state quantum simulation platform that can be controlled on the nanoscale, while a theoretical approach consists of the development of powerful numerical methods that would open the door to faster, more accurate simulations of various novel and exotic quantum systems on a classical computer.

**Related members**

- Ted Corcovilos
- Andrew Daley
- Sergey Frolov
- Edward Gerjuoy
- Peyman Givi
- Bob Griffiths
- Michael Hatridge
- Jeremy Levy
- Roger Mong
- David Pekker
- Frank Tabakin