quantum computer

• Quantum computing is computing using quantum-mechanical phenomena, such as superposition and entanglement

A quantum computer is a device that performs quantum computing.
Such a computer is completely different from binary digital electronic computers based on transistors and capacitors.
common digital computing requires that the data be encoded into binary digits (bits), each of which is always in one of two definite states (0 or 1),
quantum computation uses quantum bits or qubits, which can be in superpositions of states.

https://en.wikipedia.org/wiki/Quantum_computing

• What is a quantum computer?

A quantum computer is a device able to manipulate delicate quantum states in a controlled fashion, not dissimilar from the way an ordinary computer manipulates its bits.

What does a quantum computer look like?
A quantum computer looks like nothing you have on your desk, or in your office, or in your pocket. It is housed in a large unit known as a dilution refrigerator and is supported by multiple racks of electronic pulse-generating equipment. However, you can access our quantum computer with very familiar personal computing devices, such as laptops, tablets, and smartphones.

What is a qubit?
A qubit (pronounced “cue-bit” and short for quantum bit) is the physical carrier of quantum information. It is the quantum version of a bit and its quantum state can take values of 0, 1, or both at once, which is a phenomenon known as superposition.

What is a superposition?
A superposition is a weighted sum or difference of two or more states; for example, the state of the air when two or more musical tones are sounding at once. Ordinary, or “classical,” superpositions commonly occur in macroscopic phenomena involving waves.

How is superposition different from probability?
A set of n coins, each of which might be heads or tails, can be described as a probabilistic mixture of states, but it actually is in only one of them—we just don’t know which. For this reason quantum superposition is more powerful than classical probabilism. Quantum computers capable of holding their data in superposition can solve some problems exponentially faster than any known deterministic or probabilistic classical algorithm. A more technical difference is that while probabilities must be positive (or zero), the weights in a superposition can be positive, negative, or even complex numbers.


http://www.research.ibm.com/quantum/

• Today, real quantum computers can be accessed through the cloud, and many thousands of people have used them to learn, conduct research, and tackle new problems.

Quantum computers could one day provide breakthroughs in many disciplines, including materials and drug discovery, the optimization of complex systems, and artificial intelligence.

Quantum and Chemistry
For challenges above a certain size and complexity, we don’t have enough computational power on Earth to tackle them. To stand a chance at solving some of these complex problems, we need a new kind of computing: one whose computational power also scales exponentially as the system size grows.

What makes it ‘quantum’?
All computing systems rely on a fundamental ability to store and manipulate information. Current computers manipulate individual bits, which store information as binary 0 and 1 states.
Millions of bits work together to process and display information.
Quantum computers leverage different physical phenomena
superposition
entanglement
interference
to manipulate information.
To do this, we rely on different physical devices: quantum bits, or qubits

Superposition refers to a combination of states we would ordinarily describe independently. To make a classical analogy, if you play two musical notes at once, what you will hear is a superposition of the two notes
Entanglement is a famously counter-intuitive quantum phenomenon describing behavior we never see in the classical world. Entangled particles behave together as a system in ways that cannot be explained using classical logic
Quantum interference can be understood similarly to wave interference; when two waves are in phase, their amplitudes add, and when they are out of phase, their amplitudes cancel


In order to increase the computational power of quantum computing systems, improvements are needed along two dimensions. One is qubit count; the more qubits you have, the more states can in principle be manipulated and stored.
The second is to achieve lower error rates.
Combining these two concepts, we can create a single measure of a quantum computer’s power called quantum volume. Quantum volume measures the relationship between number and quality of qubits, circuit connectivity, and error rates of operations.

https://www.research.ibm.com/ibm-q/learn/what-is-quantum-computing/

• Quantum Computation

Rather than store information using bits represented by 0s or 1s as conventional digital computers do, quantum computers use quantum bits, or qubits, to encode information as 0s, 1s, or both at the same time.
Capabilities
Optimization
Machine learning
Sampling / Monte Carlo
Pattern recognition and anomaly detection
Cyber security
Image analysis
Financial analysis
Software / hardware verification and validation
Bioinformatics / cancer research
https://www.dwavesys.com/quantum-computing