# Quantum Computing 101 – A guide to standard Quantum Terms

Here are a few commonly used terms to learn that will help you understand Quantum Technology.

## Qubits

qubit, also known as a quantum bit, is a fundamental unit of quantum information that is physically implemented via a two-state device [1]. It serves as an extension of the bits on a classical computer. In a traditional bit, it can only have a value of 0 or 1. But a quantum computer with a quantum bit can have both values at any time [2].

There are various types of qubits, some of which exist naturally and others that are designed. The most prevalent varieties are Spin, Photons and Superconducting Circuits, Trapped Atoms, and Ions [3].

## Entanglement

Quantum entanglement happens when a group of particles is formed, interacts, or shares spatial proximity in such a way that the quantum state of each particle in the group cannot be described independently of the state of the others, even when the particles are separated by a significant distance [4].

Adjusting the state of an entangled qubit immediately changes the state of the paired qubit in quantum computers. As a result, entanglement accelerates the processing speed of quantum computers, and it is considered a fundamental property of quantum physics that is not present in classical mechanics [5].

## Quantum Circuit

quantum circuit is a type of computational procedure that combines simultaneous real-time classical computation with coherent quantum operations on quantum data like qubits. It consists of organized quantum gates, measurements, and resets that can conditionally use information from real-time classical computation [6]. Large quantum circuits are necessary to address problems that classical computers cannot handle.

One example of a quantum circuit is IBM’s Quantum Composer. This graphical quantum programming tool lets you drag and drop operations to build circuits and run them on real quantum hardware or simulators. The program can visualize qubits states, run on quantum hardware, and automatically generate the code.

## Quantum Gate

A fundamental quantum circuit that uses a series of qubits is known as a quantum logic gate (or simply a quantum gate). Just like a traditional computer’s logic gates, quantum computing has quantum circuits. Quantum logic gates, in contrast to many classical logic gates, are reversible [7]. Reversible logic gates have n inputs and n outputs or an equal number of inputs and outputs. The amount of energy lost during computations will be minimized when the number of inputs and outputs is similar [53]. A few examples of quantum gates are the Pauli Gates, Digression: The X, Y & Z-Bases, The Hadamard Gate, The I, S, and T-gates, and The P-gate.

## Quantum Algorithm

quantum algorithm is a series of steps that can be carried out on a quantum computer. The term “quantum algorithm” refers to any algorithm that appears to be inherently quantum or is used in quantum computation, such as quantum superposition or quantum entanglement [8].

One of the exciting aspects of quantum algorithms is that they can solve some problems more quickly than classical algorithms because the quantum superposition and quantum entanglement they exploit are likely inefficiently simulable by classical machines [8].

## Bloch Sphere

The Bloch sphere, which bears the name of the physicist Felix Bloch, is a geometrical illustration of the pure state space of a two-level quantum mechanical system (qubit) used in quantum mechanics and computing [9].

The Bloch sphere is a graphic depiction of a qubit’s state. It is a mathematical model of a specific quantum state of a qubit that allows researchers to identify and control different forms within the sphere [10]. The Bloch sphere is a unit 2-sphere with antipodal points that are a pair of state vectors that are orthogonal to one another. The Bloch sphere’s north and south poles are typically chosen to match the standard basis vectors display 0 and 1, which can be used to represent the spin-up and spin-down states of an electron, respectively [9].

## Qiskit Programming Framework

Founded and supported by IBM Research, Qiskit is the software that sits between quantum algorithms and hardware quantum devices. It converts popular programming languages such as Python into quantum machine language. It is an open-source SDK for interacting with quantum computers at the pulse, circuit, and application module levels.

Users of all skill levels are able to use Qiskit for research and application development because it comes with a comprehensive collection of quantum gates and a wide range of pre-built circuits. Additionally, the transpiler converts Qiskit code into an optimized course, enabling users to program for any quantum processor or processor architecture with a minimum of inputs using a backend’s native gate set [11]

Students and interested learners have access to an online digital Qiskit textbook that teaches theoretical quantum computing and the experimental quantum physics that realizes it. This course is designed on a jupyter notebook structure, allowing easy reading while allowing readers to edit and run code from within the textbook.

According to users, the qiskit textbook includes detailed directions for even the most demanding stages (e.g., setting up your API key). It is also nicely written because it is simple to understand without being bogged down by technical jargon. Another advantage is that diagrams and images allow you to follow along even if you do not have access to a computer to run the simulations yourself. I would strongly advise learning the Python programming language.

## Quantum Supremacy

Quantum Supremacy is the end goal of every quantum researcher. It is a term used by John Preskill of Caltech to characterize the demonstration of a quantum computer capable of performing tasks that are neither practicable nor possible with a conventional computer. It is the most awaited moment in the quantum industry [13].

In theory, quantum supremacy entails the engineering task of developing a powerful quantum computer and the computational-complexity-theoretic task of identifying a problem that that quantum computer can solve with a superpolynomial speedup over the best-known or possible classical algorithm for that task [14].

## Quantum Internet

The quantum internet is a system that can connect all computers around the globe; it will provide the ability to send and receive information using quantum bits (qubits) that adhere to quantum mechanics rules [15].

It could transmit massive amounts of data over vast distances at speeds exceeding the speed of light. Consider all the applications that would profit from such acceleration. Building a quantum internet is a significant goal for many countries throughout the world; such a breakthrough will provide them with a competitive advantage in a promising disruptive technology, as well as open up a new universe of innovations and limitless possibilities [16].

## Quantum Circuit Simulation

Quantum circuit modeling is critical for comprehending quantum processing and developing quantum algorithms. The quantum device in a quantum circuit is made up of N qubits, and computations are conducted by applying a series of quantum gates and measurements to the qubits.

The cuStateVec package in the NVIDIA cuQuantum SDK attempts to accelerate quantum circuit state vector simulators on GPUs. Google’s Cirq qsim simulator was one of the first to use the library, allowing Cirq customers to benefit from GPU acceleration for their existing programs. Integrations with additional quantum circuit frameworks, such as IBM’s Qiskit software, will follow [17].

## MWI Many Words Interpretation

The many-worlds interpretation (MWI), developed in 1957 by American physicist Hugh Everest, is a quantum physics interpretation that states that the universal wavefunction is objectively real and that there is no wavefunction collapse. This means that in some “world” or universe, all possible results of quantum measurements are physically realized. It means that there are most certainly an uncountably infinite number of universes. MWI views time as a many-branched tree wherein every potential quantum consequence is recognized [18].

## Copenhagen Interpretation

The Copenhagen interpretation, founded by Niels Bohr and Werner Heisenberg, is a collection of ideas concerning what quantum mechanics means. It is one of the earliest proposed interpretations of quantum physics and is still among the most often taught. The name “Copenhagen interpretation” implies more than just a spirit, such as a particular set of rules for interpreting quantum mechanics’ mathematical formalism dating back to the 1920s. [19].

The idea of complementarity is the central concept of Copenhagen’s Interpretation. Object wave and particle natures, like the two sides of a coin, can be viewed as complementary elements of a single reality. An electron, for example, can function as a wave and a particle simultaneously, much as a tossed coin can land heads or tails up, but not both at the same time [20].

## Topological Qubit

Topological qubits are a durable sort of quantum bit, first developed by Microsoft; this invention is believed to serve as the foundation for a scalable, general-purpose quantum computer system – and will represent a significant achievement in quantum physics [21].

An electron can be fragmented and present itself in various locations within a system when it is in a topological state of matter. It is more challenging to disturb an electron once separated because you need to change every location where the information is stored. Thus, it was realized that a more robust qubit with a built-in fault-tolerant feature would be more efficient. Making the task of designing a scalable, functional machine dramatically more manageable [22].

## Coherence

A qubit’s essential property is quantum coherence. Its coherence time – the duration of qubit coherence – is used to compare the quality of qubits. Coherence tells us how long a qubit keeps its information and determines its lifetime [52].

A key concept in quantum mechanics is quantum coherence, which results from quantum superposition. Quantum coherence is a crucial physical resource in quantum computation and information processing and a commonly required condition for entanglement and other kinds of quantum correlations [23].

## Quantum Dot

Quantum dots are nanoparticles with electronic characteristics that quantum mechanics governs. A pair of quantum dots can function as a single fundamental element in a quantum logic device known as a quantum bit or qubit. Silicon qubits can hold only one or a few electrons [24].

It is a nanoscale semiconductor particle with optical and electrical properties that differ from bigger particles due to quantum mechanics. They are an essential aspect of nanotechnology because of their uniqueness and the fact that they are constrained, discrete electronic states, just like naturally occurring atoms or molecules. The similarity between the electronic wave functions in quantum dots and those in actual atoms has been demonstrated [25].

## Quantum Key Distribution (QKD)

Quantum key distribution (QKD) is a secure communication technology that uses quantum physics to construct a cryptographic protocol. It allows two parties to generate a shared random secret key that is only known to them and can then be used to encrypt and decode messages. Because it is the most well-known example of a quantum cryptographic challenge, it is frequently referred to wrongly as quantum cryptography [26].

QKD generates a keying tool to protect and preserve the confidentiality of an encryption algorithm. QKD is based on physical qualities, and distinct physical layer communications provide its security. This necessitates using specialized fiber connections or the physical management of free-space transmitters. It cannot be implemented in software or as a network service, and it is challenging to integrate into the current network infrastructure. Because QKD is hardware-based, it does not allow for upgrades or security patches. Some examples of QKD protocols are BB84, Silberhorn, Decoy State, KMB09, and E91 [27].

## Quantum Sensors

Quantum sensors provide exceptional sensitivity in measuring physical parameters such as temperature, magnetic field, and rotation. Their precision is due to the sensitivity of quantum states to tiny changes in their surroundings [28]. The most sensitive gravity sensors use atom interferometry on atoms chilled to near absolute zero and in free fall. Rather than measuring the interference pattern by optical intensity, the population of two atomic states is estimated. The atoms acquire a phase difference due to gravity during the sequence, allowing us to detect local changes in density [54].

Quantum sensors can take many shapes; they are simply systems in which some particles are in such a carefully balanced state that even minor fluctuations in their exposed fields influence them [29]. One example of an application of quantum sensors is through the aerospace industry; the Quantum gravity sensors can be utilized for any activity where “you want to have a sense of the subterranean mass distribution.” This is true for hydrology and seismology.

## Universal Quantum Computer

A quantum Turing machine (QTM), also known as a universal quantum computer, is an abstract machine used to simulate the effects of a quantum computer. It provides a simple model that incorporates the full potential of quantum computation—that is, any quantum algorithm may be formally defined as a specific quantum Turing machine [30].

A universal quantum computer combines the full power of a classical computer with the power of a quantum computer, allowing simulation of physics, including and particularly quantum mechanics [31].

## QASM

Open Quantum Assembly Language (QASM) is a quantum instruction intermediate representation[32]. QASM began as a language for explicitly defining a quantum circuit to output graphics for display. The language is intended to specify quantum circuits as input to a quantum computer as quantum computation matured. A QASM program declares the classical bits and qubits, explains the operations (gates) on those qubits and measures the qubits to retrieve the classical result. Since its inception as a mark-up language for creating images, many variants of QASM have seen the light [33].

## Q#

Q# is an open-source programming language developed by Microsoft for building and running quantum algorithms. It is a Quantum Development Kit (QDK) component, an SDK that provides tools to aid you in developing quantum software.

As a programming language, Q# borrows components from Python, C#, and F# and provides a basic procedural model for constructing programs that include loops, if/then expressions, and standard data types. It also provides novel quantum-specific data structures and procedures, such as repeat-until-success and adaptive phase estimation, that enable the integration of quantum and classical calculations [35].

## Quantum Cryptography

Cryptography is a method of encrypting data or transforming plain text into scrambled text that someone with the appropriate “key can only read.” Quantum cryptography, by extension, employs quantum physics principles to encrypt and transport data in an unhackable manner [36].

The benefit of quantum cryptography is that it enables the fulfillment of many cryptographic tasks previously shown or hypothesized to be unachievable using only classical (i.e., non-quantum) communication. Quantum cryptography can encrypt data for longer lengths of time than classical cryptography. Scientists cannot guarantee encryption beyond around 30 years using conventional cryptography, but some stakeholders may require more extended periods of protection [37].

## Variational Quantum Eigensolver

The variational quantum eigensolver (VQE) is a quantum algorithm for quantum chemistry, quantum simulations, and optimization issues in quantum computing. It is a hybrid algorithm that finds the ground state of a physical system using both conventional and quantum computers [38].

The algorithm begins with an initialization, which maps configurations onto qubits, such as a portfolio’s loss functions or a molecule’s electron orbitals, and an ansatz, which is an initial parametrized initial of the wave function. VQE uses classical optimization methods to minimize the energy of the estimated state after calculating it with quantum computing [39].

## Quantum Winter

Quantum Winter is a term uniquely defining the period of stasis in quantum computing growth and decreasing funding and interest in quantum computing. In simpler terms, the end of the quantum computing era. Quantum computing has been quite popular in many industries; there have been a lot of collaborations and intended funding to advance the growth of the technologies; however, it is still yet considered in its early phases, and there has also been a lot of speculation on whether quantum computing is just a bluff.

One great example of this is the book written by a skeptic critic, Mikhail Dyakonov, a prominent professor of physics in France; his book was titled “Will We Ever Have a Quantum Computer?”, published in 2020, has seed on the idea that it is beyond impossible to attain the quantum computing we all tried to have.

Dyakonov ended his book with a notion that steered the industry [53]

“No, we will never have a quantum computer. Instead, we might have some special-task (outrageously expensive) quantum devices operating at millikelvin temperatures. The saga of quantum computing is waiting for a profound sociological analysis, and some lessons for the future should be learned from this fascinating adventure.”

The most significant hazard of a quantum winter is if research abruptly ceases, causing economic disruption and delaying discoveries that aren’t just around the corner but over the horizon. Although for some, Quantum Winter does not mean quantum computing is doomed for the rest of time; instead, it signals that one growth cycle for quantum computing has been completed [40].

## Shor’s Algorithm

Shor’s algorithm is well-known for its ability to factor integers in polynomial time. Because the most famous classical procedure takes superpolynomial time to factor the product of two primes, the commonly used cryptosystem, RSA, is based on the notion that factoring is impossible for large enough numbers. [41].

Because it is based on quantum computing, it is referred to as a quantum algorithm. The algorithm determines the prime factors of a positive integer P. Shor’s algorithm runs in polynomial time, which is polynomial in log N. On a traditional computer, the execution time is of the order O((log N)3 [42].

## Grover’s Algorithm

Grover’s algorithm, commonly known as the quantum search algorithm, is a quantum algorithm for unstructured search that finds the unique input to a black box function that yields a specific output value with high probability [43].

A quantum computer’s numerous advantage over a classical computer is its better speed when searching databases. Grover’s algorithm exemplifies this ability. This approach can quadratically speed up an unstructured search problem. Still, it may also be used as a general trick or subroutine to gain quadratic run time benefits for several different algorithms. This is referred to as the amplitude amplification trick [44].

## Error-Correction

Quantum Error Correction (QEC) is a technique used to detect and correct errors in quantum computers. It can draw on established mathematical methodologies to design special “radiation-hardened” classical microprocessors used in space or other harsh situations where faults are significantly more frequent. QEC is the source of much of the enormous potential that underpins our community’s aspirations for large-scale quantum computing [45]. The repetition code is the most well-known example of error correction, in which each bit in an input message is duplicated numerous times. For example, if you had the message 01101, we could use this repeating approach to encode it, and it would become 000 111 111 000 111 [55].

It is used to secure quantum information against errors caused by decoherence and other quantum noise. Theoretically, quantum error correction is required for fault-tolerant quantum computing, which can mitigate the impact of noise on stored quantum information, defective quantum gates, faulty quantum preparation, and erroneous measurements [46].

## Noise

The term “noise” refers to everything that causes interference in a quantum computer. A quantum computer is susceptible to interference from various sources, such as electromagnetic signals from WiFi or disturbances in the Earth’s magnetic field, just as a mobile phone call can suffer interference and cause it to break up. When qubits in a quantum computer are subjected to this type of noise, the information in them degrades in the same way that interference on a phone call degrades sound quality, commonly referred to as decoherence.

Because of the noise, the information in the qubits becomes randomized, resulting in errors in our algorithm. The greater the influence of noise, the shorter the algorithm can run before failing and producing an erroneous or meaningless result [45].

## Quantum Teleportation

Quantum teleportation transports quantum information from a sender in one location to a receiver in another. While teleportation is frequently depicted in science fiction as a method of moving physical objects from one place to another, quantum teleportation only moves quantum information [46].

Quantum teleportation is a practical method for sending quantum information over arbitrary distances without subjecting the quantum states to environmental thermal decoherence or other adverse effects. The operation of quantum computers, which manipulate quantum information and is of utmost importance, depends on quantum teleportation. Quantum internet, which refers to data transfer between nearby quantum computers, can be addressed with quantum teleportation [47].

## Quantum Communication

Quantum communication is an application of quantum physics closely related to quantum information processing and teleportation. Its most intriguing use is the use of quantum cryptography to safeguard information pathways against eavesdropping [48]. It creates ultra-secure communication channels and worldwide networks by utilizing quantum information phenomena. Potential uses include better security, privacy, cryptography, and worldwide quantum networks based on satellites [49].

## Quantum Measurement

Observing or engaging with a quantum system is performing a quantum measurement. In contrast to conventional measures, Quantum measurements result in the collapse of the quantum state, and some quantum measurement types are incompatible with one another. Quantum measurements are unpredictable, yet quantum mechanics can predict the probability [49].

With the MWI of quantum mechanics, many parallel worlds exist in the same space and time as our own. The existence of other worlds allows us to eliminate randomness and action at a distance from quantum theory and hence from all of physics. The MWI solves quantum mechanics’ measurement difficulty [56].

References:

[1] https://en.wikipedia.org/wiki/Qubit

[2] quantum-computing.ibm.com/composer/docs/iqx/guide/the-qubit

[3] https://uwaterloo.ca/institute-for-quantum-computing/quantum-101/quantum-information-science-and-technology/what-qubit

[4] https://en.wikipedia.org/wiki/Quantum_entanglement

[5] https://research.aimultiple.com/quantum-computing-entanglement/

[6] https://qiskit.org/textbook/ch-algorithms/defining-quantum-circuits.html

[7] https://en.wikipedia.org/wiki/Quantum_logic_gate

[8] https://en.wikipedia.org/wiki/Quantum_algorithm

[9] https://en.wikipedia.org/wiki/Bloch_sphere

[10] https://medium.com/quantum-untangled/quantum-states-and-the-bloch-sphere-9f3c0c445ea3

[11] https://qiskit.org/

[12] https://en.wikipedia.org/w/index.php?title=Qiskit&oldid=1117191367

[13] https://www.nist.gov/physics/introduction-new-quantum-revolution/quantum-supremacy

[14] https://en.wikipedia.org/wiki/Quantum_supremacy

[15] https://qutech.nl/research-engineering/quantum-internet/

[16] https://www.bbvaopenmind.com/en/technology/digital-world/quantum-internet-explained/

[17] https://developer.nvidia.com/blog/accelerating-quantum-circuit-simulation-with-nvidia-custatevec/#

[18] https://en.wikipedia.org/wiki/Many-worlds_interpretation

[19] https://en.wikipedia.org/wiki/Copenhagen_interpretation

[20] http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec15.html

[21] https://news.microsoft.com/features/new-microsoft-breakthroughs-general-purpose-quantum-computing-moves-closer-reality/

[22] https://news.microsoft.com/features/new-microsoft-breakthroughs-general-purpose-quantum-computing-moves-closer-reality/

[23] https://www.techopedia.com/definition/34025/quantum-coherence#

[24] https://cen.acs.org/materials/electronic-materials/Hotdots-quantum-computing/98/web/2020/04#

[25] https://en.wikipedia.org/wiki/Quantum_dot

[26] https://en.wikipedia.org/wiki/Quantum_key_distribution

[27] https://www.nsa.gov/Cybersecurity/Quantum-Key-Distribution-QKD-and-Quantum-Cryptography-QC/

[29] https://news.mit.edu/2022/quantum-sensor-frequency-0621

[30] https://en.wikipedia.org/w/index.php?title=Quantum_Turing_machine&oldid=1094087087

[31] https://jackkrupansky.medium.com/what-is-a-universal-quantum-computer-db183fd1f15a

[32] https://en.wikipedia.org/wiki/OpenQASM

[33] https://www.quantum-inspire.com/kbase/cqasm/

[34] https://learn.microsoft.com/en-us/azure/quantum/overview-what-is-qsharp-and-qdk

[35] https://quantumxc.com/blog/quantum-cryptography-explained/

[36] https://en.wikipedia.org/wiki/Quantum_cryptography

[37] https://en.wikipedia.org/wiki/Variational_quantum_eigensolver

[38] https://www.classiq.io/insights/quantum-algorithms-vqe

[39] https://jackkrupansky.medium.com/risk-is-rising-for-a-quantum-winter-for-quantum-computing-in-two-to-three-years-70b3ba974eca

[40] https://en.wikipedia.org/w/index.php?title=Shor%27s_algorithm&oldid=1125458916

[41] https://qiskit.org/textbook/ch-algorithms/shor.html

[42] https://en.wikipedia.org/wiki/Grover%27s_algorithm

[43] https://quantum-computing.ibm.com/composer/docs/iqx/guide/grovers-algorithm

[44] https://q-ctrl.com/topics/what-is-quantum-error-correction

[45]  https://en.wikipedia.org/w/index.php?title=Quantum_error_correction&oldid=1124292726

[46] https://q-ctrl.com/topics/what-is-quantum-error-correction

[47] https://en.wikipedia.org/wiki/Quantum_teleportation

[48] https://brilliant.org/wiki/quantum-teleportation/

[49] https://www.picoquant.com/applications/category/quantum-optics/quantum-communication

[50] https://uwaterloo.ca/institute-for-quantum-computing/quantum-101/quantum-101-glossary

[51] https://uwaterloo.ca/institute-for-quantum-computing/quantum-101/quantum-101-glossary

[52] https://www.qutube.nl/fundamentals-11/coherence-111

[53] http://backreaction.blogspot.com/2022/11/quantum-winter-is-coming.html

[54] https://www.birmingham.ac.uk/research/activity/gravity/quantum-sensors.aspx

[55] https://www.section.io/engineering-education/understanding-error-correcting-codes-part-1/

[56] https://plato.stanford.edu/entries/qm-manyworlds/#MeasExis