Table of Contents

- Introduction
- What is Quantum Computing
- What is the quantum computing advantage?
- What is quantum mechanics?
- What is a qubit?
- How are qubits different from classical bits?
- 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.
- Conclusion
- 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.