What is Quantum Computing? [Everything You Need to Know]

Quantum computing is a type of computation that harnesses the collective properties of quantum states, such as superposition and entanglement perform operations. 

Quantum computers, once finally realized, are not suited for all types of computational problems, but they are exceptionally well-suited for certain tasks, such as factoring large numbers, searching databases, and simulating quantum physical processes, which would be impractically slow on classical computers.

While quantum computing is still in its infancy, with many technical challenges to overcome, its development could revolutionize industries by making previously intractable problems solvable, potentially leading to breakthroughs in materials science, cryptography, drug discovery, and optimization problems in logistics and manufacturing. 

Right now, hundreds of companies and research institutions, thousands of scientists, and dozens of investment institutions are focused on bringing practical and widespread use of quantum computing to the market. The key is, more and more, you do not need to be a scientist or a quantum physicist to begin to understand quantum science and technology. In this article, we will offer the basics for people to start learning about quantum, start planning for the quantum future, and even offer ways you can become part of what might be a historic technological shift. 

What Is Quantum Computing Exactly?

Essentially, quantum computing relies on the well-established, although somewhat still mysterious, principles of quantum mechanics. This is the fundamental theory in physics that describes nature at the smallest scales of energy levels of atoms and subatomic particles. As we will discuss, aspects of quantum mechanics – specifically superposition and entanglement – offer the potential for incredible computational advantages.

Quantum information science researchers are busy trying to reliably and accurately tap into that computational potential to create quantum computers that work for real-world problems.

First, it’s important to know the basics of quantum computing.

Fundamentals of Quantum Computing

To understand quantum computing, we must first recognize critical aspects that separate it from classical computing, including qubits, superposition, and entanglement. 

Quantum Bits (Qubits) Explained

Unlike classical computers, which encode data in binary digits (bits) that are either 0s or 1s, quantum computers use quantum bits, or qubits, which, as we’ll explain shortly, can be in superpositions of states. This means a qubit can be in a state of 0, 1, or both 0 and 1 simultaneously.

Qubits are typically realized through systems that exhibit quantum mechanical behaviors, such as the spin of an electron or the polarization of a photon. Manipulating these properties with precision allows the creation and control of qubits for computation.

Qubits may sound magical, and, in a way, they are. The ability to assume a range of states, rather than a binary, on-off, yes-no, either-or state offers amazing computational properties. But, alas, qubits aren’t perfect. They are extremely delicate and can be easily disturbed by their environment—it’s a challenging state for quantum scientists who normally refer to it as decoherence. This sensitivity requires that quantum computations are performed within extremely short timescales and often at very low temperatures to maintain the qubits’ quantum state. Developing stable qubits that can maintain their state long enough to perform useful computations is one of the central challenges in the field of quantum computing.

You may also be interested: Quantum Information Processing: From Bits To Qubits

Principles of Superposition and Entanglement

Two principles of quantum mechanics lie at the heart of quantum computation: superposition and entanglement.

As mentioned, classical computing bits are in either a 1 or 0 position – think of a light switch in either the on or off position. Superposition in quantum mechanics, on the other hand, is a principle where a quantum system can exist in multiple states or configurations simultaneously. Analogies often fail to fully conceptualize the nuance of superposition, but consider a light that doesn’t have a switch, but uses a dimmer that can adjust the light between on and off. Or, you could visualize it as a coin spinning incredibly fast. It’s both in the heads and tails position until someone stops the spin and observes the eventual position of the coin.

Entanglement extends the power of superposition. When qubits are entangled, the state of one qubit can depend on the state of another, no matter how far they are separated in space. This leads to a phenomenon where the information capacity of a quantum system can grow exponentially with the number of qubits because they can perform many calculations at once.

Read also: How Can Quantum Entanglement Be Used For Secure Communication?

How does Quantum Computing Work?

Let’s remember our discussion about classical bits. Bits are easily manipulated with digital gates.

However, qubits are different. They must be manipulated with quantum gates in a quantum circuit. These gates change the probabilities of a qubit’s state without necessarily measuring its value, thus enabling complex computations.

Here’s how this works.

Quantum Gates and Circuits

Quantum Gates: Because qubits can exist in superpositions of states, quantum gates manipulate these qubits through operations that are typically represented by matrices, which are rectangular arrays of numbers, or symbols, arranged in rows and columns that are often to represent and manipulate data. The operations include rotation of the state (changing the probabilities of a qubit being in the 0 or 1 state), entanglement (linking the states of two qubits such that the state of one depends on the state of the other), and superposition (creating a state where the qubit is in a combination of 0 and 1).

Wikipedia

Quantum Circuits: A quantum circuit is a sequence of quantum gates, designed to perform a specific computation. The qubits pass through these gates in a manner that’s conceptually similar to how bits pass through classical gates in a conventional circuit. However, due to the quantum nature of these circuits, they can perform complex computations more efficiently than classical circuits, especially for certain problems like factoring large numbers or simulating quantum systems.

IBM Quantum Circuit – Research Gate 

Quantum circuits have to be carefully designed to account for quantum phenomena like coherence and entanglement. Additionally, measurements in quantum computing are fundamentally different from classical computing. When a qubit is measured, its superposition collapses to one of the basis states (0 or 1), affecting the outcome of the computation.

The Quantum Computing Process: From Theory to Application

We should start with the well-established – yet still quite vexing – theoretical foundations. Quantum computing is rooted in quantum mechanics, the branch of physics that deals with the behavior of particles at the atomic and subatomic levels, which is a little over a century old. The key theoretical principles that guide quantum mechanics – including, as discussed, superposition and entanglement – not surprisingly underpin quantum mechanical applications, including technologies like quantum computing.

As can be gathered, the quantum computing process, from theory to application, involves several complex and interconnected steps – from the physical realization of qubits to the design of quantum gates and circuits to the creation of error correction schemes to the development of quantum algorithms. 

The goal, of course, is to create quantum computers for potential applications in various fields like cryptography, drug discovery, optimization problems, financial modeling, and more. 

Quantum computing, though, is still in a relatively early stage. Ongoing research is focused on creating more stable qubits, scaling up the number of qubits, improving error correction, and developing new algorithms and applications.

But, you’re probably asking why all the efforts to create quantum computers when technologies are doing pretty well with classical computers and even better with classical supercomputers.

Now, forgive the mixing of hypothetical and theoretical possibilities here, but quantum computers could vastly outpace classical computers at many tasks – and even vastly outperform today’s supercomputers.

We’ll look at those potential capabilities now. 

Comparing Quantum and Classical Computing

Most scientists believe that robust fault-tolerant quantum computers will be able to outperform classical computing approaches in many – but not all – tasks. Specifically, quantum devices have an advantage in calculations, such as optimization, simulation, and various cryptographic functions.

Speed and Efficiency: The Quantum Advantage

For those tasks, quantum computers, buoyed by superposition and entanglement, are recognized as game-changing calculation machines with unprecedented speed and efficiency. Superposition offers quantum computers a path toward parallelism that can boost speeds while entanglement offers an increase in efficiency that classical computers can’t match because they must process each bit independently.

Limitations and Challenges in Quantum Computing

With such speed and efficiency, there must be a reason why the devices are not in use today. There are several limitations and challenges in quantum computing. First, is the sheer complexity of the devices. All approaches to quantum computing require highly sensitive equipment and intense engineering, even when compared to the most advanced supercomputers. The main limitation and challenge in quantum computing, however, is the vulnerability to environmental noise. Because qubits are ultra-sensitive to interference from, for example, heat, and electromagnetism (even cosmic rays), qubits can produce errors that affect a quantum computer’s ability to make efficient, speedy calculations. Therefore, great care must be taken to preserve those quantum states as long as possible. This explains most of the need for the complex engineering of the devices. But scientists must also design error-correction protocols to minimize this tendency to make errors. Although teams are making rapid progress, classical computers still have an advantage over solving most problems – and all practical problems – due to their stability when compared to quantum computers.

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Applications of Quantum Computing

While we must realize there are challenges to practical quantum computing, teams of scientists are making progress toward realizing fault-tolerant quantum computing, If they ultimately succeed, there are several initial applications of quantum computing. We’ll look at some of the most probable quantum computing applications and use cases next.

1. Cryptography and Cybersecurity Enhancements

Quantum computing has profound implications for cryptography and cybersecurity. Traditional encryption methods, like RSA, rely on the difficulty of factoring large numbers, a task that quantum computers could perform exponentially faster. This capability threatens current encryption standards, necessitating the development of quantum-resistant cryptography. Conversely, quantum computing introduces advanced cryptographic techniques, such as quantum key distribution (QKD), which offers theoretically unbreakable encryption. QKD uses quantum properties like entanglement and superposition to detect any attempt at interception, thus ensuring absolute security in data transmission. Quantum computers also enhance cybersecurity by analyzing vast datasets to identify patterns and potential threats far more efficiently than classical computers. This ability to rapidly process and analyze large amounts of data can significantly improve real-time threat detection and response, making cybersecurity systems much more robust and reactive.

See also: What Is Quantum Security And How Does It Work?

2. Breakthroughs in Drug Discovery and Material Science

In drug discovery and material science, quantum computing enables simulations of molecular and chemical interactions at an unprecedented level of detail. Traditional computers struggle to simulate complex molecules due to the exponential increase in variables, but quantum computers can handle such complexity with relative ease. This capability allows for accurate modeling of molecular structures and behaviors, leading to faster and more efficient drug discovery processes. For instance, quantum computers can rapidly analyze and predict how different drug compounds will interact with specific biological targets, thereby speeding up the identification of promising drug candidates and reducing reliance on trial-and-error methods. In material science, quantum simulations can lead to the discovery of new materials with desired properties, such as higher strength-to-weight ratios or better electrical conductivity. This can revolutionize industries like aerospace, electronics, and renewable energy by enabling the creation of more efficient, sustainable, and cost-effective materials.

3. Optimizing Complex Systems: From Finance to Logistics

In finance and logistics, quantum computing offers significant improvements in optimizing complex systems. In finance, quantum algorithms can optimize investment portfolios by analyzing vast amounts of market data and simulating numerous financial scenarios simultaneously. This can lead to more robust risk assessment models and enhanced asset allocation strategies, maximizing returns while minimizing risks. Quantum computing also accelerates option pricing models and other complex financial calculations, providing a competitive edge in high-frequency trading. In logistics, quantum computing can optimize supply chain management by solving complex routing problems much more efficiently than classical computers. This includes determining the most efficient routes for transportation, minimizing delivery times, and reducing costs. For large-scale logistics operations, such as global shipping or airline scheduling, the optimization capabilities of quantum computing can result in significant improvements in efficiency, cost savings, and environmental sustainability.

See also: 5 Crucial Quantum Computing Applications & Examples

Where is Quantum Computing At The Moment

The joke in quantum computing was that it was 20 years away – and that it’s always 20 years away. That joke is seen as less funny now because of the steady stream of advances in quantum information sciences that have put the industry on the cusp of creating devices that have real-world advantages. Private capital and government investment have provided more research and created increasing incentives to develop the theoretical and practical underpinnings of quantum devices that can produce practical advantages. While timelines are impossible to reliably construct, the roadmaps of many quantum computing companies see quantum advantage by the end of the decade and, among the more audacious, within three to five years.

Leading Players in the Quantum Computing Field

As you might expect, the leaders in the quantum tech field are also leaders in our tech-centric economy, namely IBM, Google, Microsoft, and Amazon, especially through its Amazon Web Services, or AWS division.

However, several hardware, software, and full-stack quantum computing companies have appeared in the industry.

Here are a few:

Rigetti Computing 

Specializing in integrated quantum computing systems, Rigetti Computing is known for fabricating quantum chips and developing full-stack software.

IonQ 

This company focuses on trapped ion quantum computing technology, known for its high-fidelity quantum gates and scalable architecture.

PsiQuantum

PsiQuantum is working toward a silicon photonic quantum computer, aiming for a machine with a million qubits.

D-Wave Systems

Known for its quantum annealing technology, D-Wave primarily focuses on optimization problems. D-Wave has undertaken a program that will build and deliver a scalable gate-model quantum computing technology.

Oxford Quantum Circuits (OQC)

Founded in 2017 as a spin-out from the University of Oxford, Oxford Quantum Circuits is one of the UK’s leading quantum computing companies. 

QC Ware

This company develops software for quantum computing, aiming to make quantum computing easily accessible to classical computer programmers.

Alice & Bob

Alice & Bob aims to build a fault-tolerant quantum computer, focusing on addressing qubit errors.

Xanadu Quantum Technologies

Specializing in photonic quantum computing, Xanadu Quantum Technologies is known for its cloud-based quantum computing platform and quantum machine learning algorithms.

QuTech

A collaboration between TU Delft and TNO, focusing on both quantum computing and quantum internet technologies.

Quantinuum 

Formed from the merger of Honeywell Quantum Solutions and Cambridge Quantum, Quantinuum focuses on creating scalable, error-corrected quantum computing solutions and offers a comprehensive suite of quantum software.

Each of these companies is contributing significantly to the advancement of quantum computing technology, with varied focuses ranging from hardware to software and specific applications in quantum computing.

If you are interested in a more complete list of quantum computing companies, check out Quantum Computing Companies: A Full 2024 List.

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Recent Developments and Breakthroughs

In the past few years, as larger investment amounts have flowed into quantum and more researchers have turned their attention to challenges facing quantum computing and other forms of quantum technology, we have seen an increase in the number of research advances, often called research breakthroughs, and business developments.

Here are just a few of the recent advances that might be considered historic quantum computing developments and breakthroughs.

Quantum Computing Advances: A pivotal development in quantum computing was Google’s 2019 declaration of quantum supremacy. Quantum supremacy is a term used to describe a task that far exceeds the abilities of a classical computer or even a supercomputer. In this case, the task was a random quantum circuit sampling task performed on Google’s 53-qubit quantum processor named Sycamore, which would have taken classical supercomputers 10,000 years to complete. 

Following Google’s announcement of quantum supremacy, IBM has made significant strides in the field of quantum computing. In 2021, they unveiled a 127-qubit quantum processor named ‘Eagle’, marking a significant step forward in quantum capability. This processor is designed to handle more complex computations and represents a critical milestone towards practical quantum computing. Recently the company announced a 1,000-plus qubit quantum computer and detailed strides in a model that better resists errors.

Quantum Internet Advances: In 2021, scientists at Delft University of Technology in the Netherlands successfully established a multi-node quantum network, laying the groundwork for a future quantum internet. This network, connecting three quantum processors, demonstrated the potential for quantum systems to communicate over distances, a development that could revolutionize data security and connectivity.

Quantum Error-Correction Advances:  QuEra Computing announced a significant advance in error correction that was published in the scientific journal Nature. In experiments led by Harvard University in close collaboration with QuEra Computing, MIT, and NIST/UMD, researchers successfully executed large-scale algorithms on an error-corrected quantum computer with 48 logical qubits and hundreds of entangling logical operations

Topological Quantum Computers: Topological quantum computers represent an interesting approach to fault tolerance, a way to avoid the debilitating effects of errors in quantum computation. In 2023, Quantinuum announced a step toward fault-tolerant quantum computing. This achievement was enabled by the release of Quantinuum’s System Model H2.

The Future of Quantum Computing

In a Churchillian twist, experts often say that we are not at the end of our journey in building quantum computers for practical purposes, or even at the beginning of the end, but we may be near the end of the beginning of that era. While it’s impossible to predict accurate timelines for the evolution of this swiftly emerging and erratically transforming technology, here are some milestones we should anticipate in the coming years.

Predictions and Potential Impacts

Despite the optimization, there are still hurdles that remain. Error correction remains a difficult problem for quantum scientists and engineers working to bring quantum computing into practical use. In the near future there will be ongoing efforts to master error correction.

As error correction is mastered, fault tolerance – which includes quantum computers designed to prevent and correct errors due to quantum decoherence and other quantum noise – becomes more and more a possibility.

If all goes right, we should expect to see quantum computers, slowly but surely, being used as part of the computer options for research institutes and companies. In the long term, hybrid quantum-classical data centers will tackle major challenges that are facing science and society. This means quantum computers will play a role in finding new treatments and pharmaceuticals, devising new portfolio optimization strategies, and discovering new climate-saving materials, among other profound benefits.

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Ethical and Societal Considerations

With great power comes great responsibility, an admonition, often sourced to Spiderman, that could be applied with equal vigor to the superhero of the computational space: quantum computing. Ethical and societal considerations are of great concern to the quantum computing community.

Two primary, although certainly, not exclusive, ethical and societal concerns are the wariness about the power of quantum computing resting in too few hands and the concern that the potential of quantum computing’s hacking ability may be tapped by bad actors.

In the former, members of the quantum computing community want to ensure that there are efforts to democratize quantum. This article, for example, is designed to make quantum computing understandable and actionable to as many people as possible, not just people who have mastered quantum information science and developers who can write quantum algorithms. Although education is important, tools need to be created to let non-scientists interact with quantum computers, and access to these devices – such as through cloud-based services – must also be ensured. 

In the latter, the amazing number-crunching power of quantum computers, which can be used to find new drug therapies and help balance our portfolios, can also be used to crack most of the cryptographic schemes used to keep data and information safe. Right now, scientists are working on quantum-safe cryptographic techniques to protect data and stave off what could be the collapse of financial systems and societal trust networks.

Getting Started with Quantum Computing

One of the misconceptions about quantum computing is that only physicists understand quantum computing and should be concerned about quantum computing. No matter what your skill level in science and math, with an open mind and an eager curiosity, you can begin to learn more about quantum computing and how it could affect our lives, society, and future. There are many paths to learn about quantum computing and many educational resources – from free, learn-at-your-convenience programs to formal programs at the world’s leading institutions. Here are just a few:

Educational Resources and Learning Paths

At one time, the educational path to attain an understanding, let alone mastery, of quantum computing was fairly rigid. You spend four to six years in a physics program attaining undergraduate- and master-level certificates. Then, you likely entered a doctoral program where you focused your studies on quantum information science. Your added challenge was that most universities did not have this field of study, or were not sufficiently strong in QIS. Obviously, this was an expensive journey.

However, now, depending on your current educational status and your current goals, you can find quantum educational resources to suit you. Many of these opportunities are inexpensive, if not free, and many are available online.

Check out our curated list of 7 Best Quantum Computing Books, complete with rankings and reviews.

Here are some book recommendations for beginners:

Quantum Computing for Everyone (Mit Press) Paperback by Chris Bernhardt

Dancing With Qubits: How Quantum Computing Works and How It Can Change The World  (Packt Publishing) by Robert S. Sutor

Quantum Computing for Babies by Chris Ferrie and William ‘whurley’ Hurley

There are also books for intermediate and more serious students of quantum computing:

Quantum Computing Fundamentals by Chuck Easttom

Fundamentals of Quantum Computing, Theory and Practice by Venkateswaran Kasirajan

We recommend exploring our list of 8 Online Quantum Computing Courses to kickstart your career in this exciting field.

Here are some other FREE quantum computing course suggestions:

The University of Queensland offers UQx: Quantum Technologies for Decision Maker (free to audit, inexpensive for verification.)

Purdue offers a MicroMasters® Program in Quantum Technology: Computing

TUDelft offers Quantum 101: Quantum Computing & Quantum Internet

LinuxFoundationX offers Introduction to Quantum Circuits

Careers and Opportunities in Quantum Computing

One of the critical challenges of quantum computing isn’t technical limitations – error correction, qubit number, etc. – it’s human limitations. Currently, there’s simply not enough trained quantum workers to support the industry’s growth. While that may be a problem, it is also an opportunity. Should a robust quantum computing industry form, companies, and organizations will need trained quantum scientists, physicists, and engineers. The industry will also require salespeople, marketers and public relations specialists, lobbyists, and executives, all with an understanding of quantum’s capabilities.

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The Ongoing Journey of Quantum Computing Innovation

To paraphrase Winston Churchill, we are not at the end of our quantum computing journey. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.

Many challenges lie ahead – and these challenges may be more vexing than ones faced by other

        Summary of Key Points

• Quantum Computers use quantum states like superposition and entanglement for operations, offering unique advantages over classical computing for specific tasks.
• Quantum computing shows promise in areas like large-number factoring, database searching, and quantum physical process simulations.
• Numerous companies, research institutions, and investors are actively engaged in developing practical quantum computing applications.
• Quantum computing is grounded in quantum mechanics, which deals with the behavior of particles at the smallest scales. These principles enable quantum computers to perform complex computations efficiently.
• Quantum computers use qubits which can exist in multiple states simultaneously, unlike classical binary bits.
• Qubits are sensitive to environmental disturbances (decoherence), requiring rapid computations and often low temperatures to maintain stability.
• Quantum gates and circuits manipulate qubits, which are essential for enabling quantum computations.
• Quantum Advantage is a point at which quantum devices offer unprecedented speed and efficiency for certain calculations, benefiting from parallelism and increased computational capacity. If this level of performance is achieved, quantum computers could be vastly better than classical computers at solving certain problems.
• Quantum computing faces significant hurdles such as complexity, environmental sensitivity, and error-proneness. 
• Quantum computing offers several opportunities and creates certain problems. They pose both threats and opportunities for encryption and security, including the development of quantum-resistant cryptography and quantum key distribution. On the other hand, QCs could enable detailed simulations of molecular interactions, potentially revolutionizing these fields.
• Quantum computing can significantly improve efficiency in fields like finance and logistics.
• Advancements and investments are bringing the field closer to practical applications, with significant progress made by leading companies.
• Companies like IBM, Google, Microsoft, and Amazon, along with other specialized firms, are key contributors to quantum computing development.
• Major milestones include Google’s quantum supremacy, advancements in quantum processors, and quantum internet experiments.
• Concerns about quantum computers include the democratization of quantum computing access and the potential misuse of its capabilities, particularly in cryptography.
• Quantum computing continues to evolve, facing numerous challenges but also offering transformative potential in various domains.

What is Quantum Computing FAQs

What is Quantum Computing?

Answer: Quantum computing is a type of computing that uses quantum-mechanical phenomena, such as superposition and entanglement, to perform operations on data. In classical computing, data is processed using binary bits (0s and 1s). In contrast, quantum computing uses quantum bits or qubits, which can probabilistically exist in multiple states simultaneously, allowing quantum computers to process a vast number of calculations at once.

How does a Quantum Computer work?

Answer: A quantum computer works by manipulating qubits through quantum gates in a quantum circuit. Unlike classical bits, qubits can be in a state of 0, 1, or any quantum superposition of these states. This allows quantum computers to perform complex calculations more efficiently than classical computers for certain problems. The operations of quantum computing are also influenced by entanglement, a property that allows qubits that are entangled to be in a correlated state.

What are the potential applications of Quantum Computing?

Answer: Quantum computing has potential applications in various fields including cryptography, drug discovery, optimization problems, financial modeling, machine learning, and materials science. Its ability to quickly process and analyze large volumes of data makes it promising for solving complex problems that are currently impractical for classical computers.

What are the challenges facing Quantum Computing?

Answer: Quantum computing faces several challenges, including error rates and qubit coherence. Quantum systems are extremely sensitive to their environment, which can lead to errors and loss of coherence. Maintaining qubits in a stable state (quantum decoherence) and error correction are significant challenges. Additionally, developing scalable quantum systems and creating useful algorithms are ongoing challenges in the field.

Is Quantum Computing a threat to current encryption methods?

Answer: Currently, no. However, quantum computing, once robust enough, could potentially break many of the current cryptographic algorithms, such as RSA and ECC, which secure digital communications. This is because quantum computers, once they reach sufficient maturity, could perform calculations, like factoring large numbers, much faster than classical computers. However, this threat has led to the development of quantum-resistant cryptography, which aims to develop new algorithms that could be secure against quantum attacks.