Quantum computing is a multidisciplinary field  comprising aspects of computer science, physics, and mathematics that  utilizes quantum mechanics to solve complex problems faster than on  classical computers. The field of quantum computing includes hardware  research and application development. Quantum computers are able to  solve certain types of problems faster than classical computers by  taking advantage of quantum mechanical effects, such as superposition  and quantum interference. Some applications where quantum computers can  provide such a speed boost include machine learning (ML),  optimization, and simulation of physical systems. Eventual use cases  could be portfolio optimization in finance or the simulation of chemical  systems, solving problems that are currently impossible for even the  most powerful supercomputers on the market.

What is the quantum computing advantage?

Currently, no quantum computer can perform a useful  task faster, cheaper, or more efficiently than a classical computer.  Quantum advantage is the threshold where we have built a quantum system  that can perform operations that the best possible classical computer  cannot simulate in any kind of reasonable time.

What is quantum mechanics?

Quantum mechanics is the area of physics that studies  the behavior of particles at a microscopic level. At subatomic levels,  the equations that describe how particles behave is different from those  that describe the macroscopic world around us. Quantum computers take  advantage of these behaviors to perform computations in a completely new  way.

What are the principles of quantum computing?

A quantum computer works using quantum principles.  Quantum principles require a new dictionary of terms to be fully  understood, terms that include superposition, entanglement, and  decoherence. Let's understand these principles below.

Superposition

Superposition states that, much like waves in  classical physics, you can add two or more quantum states and the result  will be another valid quantum state. Conversely, you can also represent  every quantum state as a sum of two or more other distinct states. This  superposition of qubits gives quantum computers their inherent  parallelism, allowing them to process millions of operations  simultaneously.

Entanglement

Quantum entanglement occurs when two systems link so  closely that knowledge about one gives you immediate knowledge about the  other, no matter how far apart they are. Quantum processors can draw  conclusions about one particle by measuring another one. For example,  they can determine that if one qubit spins upward, the other will always  spin downward, and vice versa. Quantum entanglement allows quantum  computers to solve complex problems faster.

When a quantum state is measured, the wavefunction  collapses and you measure the state as either a zero or a one. In this  known or deterministic state, the qubit acts as a classical bit.  Entanglement is the ability of qubits to correlate their state with  other qubits.

Decoherence

Decoherence is the loss of the quantum state in a  qubit. Environmental factors, like radiation, can cause the quantum  state of the qubits to collapse. A large engineering challenge in  constructing a quantum computer is designing the various features that  attempt to delay decoherence of the state, such as building specialty  structures that shield the qubits from external fields.

What are the components of a quantum computer?

Quantum computers have hardware and software, similar to a classical computer.

Quantum hardware

Quantum hardware has three main components.

Quantum data plane

The quantum data plane is the core of the quantum  computer and includes the physical qubits and the structures required to  hold them in place.

Control and measurement plane

The control and measurement plane converts digital  signals into analog or wave control signals. These analog signals  perform the operations on the qubits in the quantum data plane.

Control processor plane and host processor

The control processor plane implements the quantum  algorithm or sequence of operations. The host processor interacts with  the quantum software and provides a digital signal or classical bits  sequence to the control and measurement plane.

Quantum software

Quantum software implements unique quantum algorithms  using quantum circuits. A quantum circuit is a computing routine that  defines a series of logical quantum operations on the underlying qubits.  Developers can use various software development tools and libraries to  code quantum algorithms.

What are the types of quantum technology?

No one has shown the best way to build a  fault-tolerant quantum computer, and multiple companies and research  groups are investigating different types of qubits. We give a brief  example of some of these qubit technologies below.

Gate-based ion trap processors

A gate-based quantum computer is a device that takes  input data and transforms it according to a predefined unitary  operation. The operation is typically represented by a quantum circuit  and is analogous to gate operations in traditional electronics. However,  quantum gates are totally different from electronic gates.

Trapped ion quantum computers implement qubits using  electronic states of charged atoms called ions. The ions are confined  and suspended above the microfabricated trap using electromagnetic  fields. Trapped-ion based systems apply quantum gates using lasers to  manipulate the electronic state of the ion.  Trapped ion qubits use  atoms that come from nature, rather than manufacturing the qubits  synthetically.

Gate-based superconducting processors

Superconductivity is a set of physical properties  that you can observe in certain materials like mercury and helium at  very low temperatures. In these materials, you can observe a  characteristic critical temperature below which electrical resistance is  zero and magnetic flux fields are expelled. An electric current through  a loop of superconducting wire can persist indefinitely with no power  source.

Superconducting quantum computing is an  implementation of a quantum computer in superconducting electronic  circuits. Superconducting qubits are built with superconducting electric  circuits that operate at cryogenic temperatures.

Photonic processors

A quantum photonic processor is a device that  manipulates light for computations. Photonic quantum computers use  quantum light sources that emit squeezed-light pulses, with qubit  equivalents that correspond to modes of a continuous operator, such as  position or momentum.

Neutral atom processors

Neutral atom qubit technology is similar to trapped  ion technology. However, it uses light instead of electromagnetic forces  to trap the qubit and hold it in position. The atoms are not charged  and the circuits can operate at room temperatures

Rydberg atom processors

A Rydberg atom is an excited atom with one or more  electrons that are further away from the nucleus, on average. Rydberg  atoms have a number of peculiar properties including an exaggerated  response to electric and magnetic fields, and long life. When used as  qubits, they offer strong and controllable atomic interactions that you  can tune by selecting different states.

Quantum annealers

Quantum annealing uses a physical process to place a  quantum system's qubits in an absolute energy minimum. From there, the  hardware gently alters the system's configuration so that its energy  landscape reflects the problem that needs to be solved. The advantage of  quantum annealers is that the number of qubits can be much larger than  those available in a gate-based system. However, their use is limited to  specific cases only.