| title | description | author | ms.author | ms.date | ms.topic | uid |
|---|---|---|---|---|---|---|
What is quantum computing? |
Learn what quantum computing is, and what a quantum computer can do |
natke |
nakersha |
10/14/2019 |
article |
microsoft.quantum.overview.what |
Quantum computing is a model of computation based on the underlying logic of quantum physics.
The theory of quantum physics posits that matter, at a quantum level can be in a superposition of multiple classical states. And those many states interfere with each other like waves in a tide pool.
Quantum computing stores information in quantum states of matter and uses quantum operations to compute on that information, by harnessing and learning to program quantum interference.
Quantum computing might sound daunting, but with the right resources you can start building quantum applications today.
In quantum computing, a quantum bit - qubit - is a unit of quantum information, like a classical bit. Where classical bits hold a single binary value such as a 0 or 1, the state of a qubit is between the values of 0 and 1. This is called superposition.
The act of measurement changes a qubit. It goes from being in superposition to one of the binary states of 0 or 1. Again, measurement of a qubit is unlike a classical bit, which when 0 is measured as 0, and when 1 is measured as 1.
Qubits can also be entangled: when we make a measurement of one entangled qubit, our knowledge of the state of the other is updated, even if the qubits are physically far apart.
Quantum algorithms can be designed to take advantage of qubit superposition and entanglement to speed up classical algorithms, or to provide entirely new ways of modeling physical systems.
When multiple qubits act coherently, they can process multiple options simultaneously. This allows them to process information in a fraction of the time it would take even the fastest non-quantum systems.
One of the most famous quantum algorithms is Shor's algorithm for factorization, which makes the classically intractable problem of factorization of a large number into two prime numbers fast enough to challenge traditional cryptography.
On the more constructive side, algorithms for secure cryptographic key distribution are made possible by superposition, quantum entanglement, and the no cloning property of qubits: the inability for qubits to be copied without detection.
Grover's algorithm provides a quadratic factor speed-up for database searching.
Using quantum programs to model quantum systems themselves is another application of quantum computing. Photosynthesis, superconductors, and complex molecules are examples of quantum systems that can be simulated using quantum programs.
In classical computers, bits correspond to voltage levels in silicon circuits. Quantum computing hardware can be implemented by many different physical realizations of qubits: trapped ions, superconducting, neutral atoms, electron spin, light polarization, topological qubits. Quantum hardware is an emergent technology. It requires balancing fidelity of the system with scalability. The larger the scale (that is, number of qubits), the higher the error rate.
Up to a certain scale (number of qubits), quantum computing can be simulated on a classical computer. Using simulations is how you can start to write quantum programs using Microsoft Quantum, the Quantum Development Kit (QDK), and the Q# language.
- What can I do with a quantum computer
- Get started with the Microsoft Quantum Development Kit