quantum information and quantum computation

Their quantum state is extremely fragile. The interaction of qubits with their environment in ways that cause their quantum behavior to decay and ultimately disappear is called decoherence. The bad news is that quantum machines are way more error-prone than classical computers because of decoherence. The machines’ ability to speed up calculations using specially designed quantum algorithms is why there’s so much buzz about their potential. Quantum computers harness entangled qubits in a kind of quantum daisy chain to work their magic. But thanks to entanglement, adding extra qubits to a quantum machine produces an exponential increase in its number-crunching ability. In a conventional computer, doubling the number of bits doubles its processing power. It even baffled Einstein, who famously described it as “spooky action at a distance.” But it’s key to the power of quantum computers.

Nobody really knows quite how or why entanglement works. This happens even if they are separated by very long distances. Changing the state of one of the qubits will instantaneously change the state of the other one in a predictable way. Researchers can generate pairs of qubits that are “entangled,” which means the two members of a pair exist in a single quantum state. One of those properties is known as superposition and another is called entanglement. Qubits have some quirky quantum properties that mean a connected group of them can provide way more processing power than the same number of binary bits. In both cases, the goal is to isolate the qubits in a controlled quantum state. Others, like IonQ, trap individual atoms in electromagnetic fields on a silicon chip in ultra-high-vacuum chambers. Some companies, such as IBM, Google, and Rigetti Computing, use superconducting circuits cooled to temperatures colder than deep space.

Generating and managing qubits is a scientific and engineering challenge. Quantum computers, on the other hand, use qubits, which are typically subatomic particles such as electrons or photons. Everything from your tweets and e-mails to your iTunes songs and YouTube videos are essentially long strings of these binary digits. Today's computers use bits-a stream of electrical or optical pulses representing 1s or 0s.

Quantum information and quantum computation