The term "quantum computing" may sound like something you usually hear and see in a sci-fi movie. However, the first models of such a machine were introduced in the 1980s, so at least the quantum computer concept is not new. Operating with classical bits, traditional computing systems have served us well for decades, but they encounter limitations when confronted with highly intricate problems.

Quantum computing, on the other hand, offers a compelling promise: the ability to solve problems once deemed unsolvable at once inconceivable speeds. McKinsey & Company, a global management consulting firm, has identified it as one of the next big trends in tech that could account for nearly $1.3 trillion in value by 2035. In this article, we'll dive into the foundational concepts of quantum computing and explore the vast potential such systems offer across different fields.

## When Bits Aren’t Enough, Qubits Are Coming to Rescue

A **quantum computer** is a machine that uses unique quantum mechanical effects to perform special types of calculations that cannot be performed on classical computers. The capabilities of quantum mechanics combined with information science are studied by **quantum information science**. It clarifies in practice the meaning of such processes as decoherence or quantum entanglement without delving into complex mathematics or philosophizing about how people copycat the most complex creatures of nature.

Classical computers operate with primitive units of information called bits. Such systems can take on discrete values of 0 or 1. What makes quantum computing so unique is its possibility to operate with so-called **qubits**, subatomic particles such as electrons or photons. They can be in a superposition of the states 0 and 1. Here, superposition does not mean "0 and 1 at the same time" or "numbers between 0 and 1," as one may think. It's the ratio of the probabilities of getting one of these results equal to 1. The state of a qubit can be represented by a point on the unit sphere with the North and South poles corresponding to the states 0 and 1 of a classical bit.

*Source: Quantum Computing at the Frontiers of Biological Sciences*

Therefore, superposition means that a photon in such a system may, for example, have a 20% probability of receiving an upper spin (equal to "0") and an 80% probability of receiving a lower one (equal to "1"). Whereas N bits can represent N binary values, N qubits can represent 2N values, making them a decent basis for labor-intensive calculations.

## What Makes Quantum Computing So Special?

**Physical implementation**. In a classical computer, one bit physically corresponds to one semiconductor transistor working as a switch between 0 and 1, depending on the electric charge. For qubits, quantum objects are used. Such objects can be:

*Superconducting Qubits*based on Josephson junction. Currents on crystals maintain a superposition no longer than 10 microseconds;*Photonic Qubits*. Generation of entangled light quanta using bulky and complex optical equipment and their control for up to several hours at room temperature;*Ion Qubits in Magnetic Traps*. A chain of ions is held using an electromagnetic field system in an ultracold vacuum for up to several minutes;*Quantum Dots*on semiconductors, controlled by an electromagnetic field or laser pulses;*Quasiparticles*in topological quantum computers. Collective states of clusters of electrons, “frozen” photons or Majorana fermions, behaving like particles inside semiconductors or superconductors.

The list of quantum processors that you can find on Wikipedia contains more info about how different quantum processors are implemented. As you can see there, superconducting quantum computing is the leading type of technology for these systems.

**Entanglement**. In a classical computer, you gather as many transistors as possible and connect them using conductors. In quantum computing, qubits become entangled with each other by nonlocal correlations. Entanglement is the basis of quantum superdense coding, which allows two bits of classical information to be transmitted using a single qubit. In quantum systems, Qubits can be entangled with each other in many ways, and the number of these ways increases exponentially as the number of qubits themselves increases.

**Computing power**. A classical computer has physical limits on the speed of calculations and the size of microchips. Adding one transistor adds one extra bit you can operate, but adding one qubit into a quantum computing system doubles your computing possibilities. One qubit has only two states (0 and 1), whereas 10 qubits already have 210 = 1024 states. The superposition of these states allows you to perform many calculations in parallel with different initial data. Still, the output can only be one random result if you do not have a suitable algorithm. The limit on the amount of classical information that can be extracted from a qubit is called the Holevo's bound.

**Logical operations**. A logic gate is a device serving as a building block for digital circuits. It performs such operations as AND, OR, NOT, and others. Quantum computing has its own logic gates, which differ from those in a classical computer. In particular, in a quantum computing system, all operations are reversible (unitary) except the measurement operation, which extracts classical information from the qubit. Therefore, in quantum computing, the operations "and," "or" and copying the state of a qubit are impossible, but there are three different ways of inversion.

**Algorithms** are assembled from logic gates and allow carrying out various calculations. The following algorithms have been developed for quantum computing:

*Shor's algorithm*is used for factorization, the process of decomposition of a number into prime factors;*Grover's algorithm*solves the brute-force problem, fast search in an unordered database;*Deutsch-Jozsa algorithm*answers the question of whether a function of a binary variable is constant or balanced;*Zalka-Wiesner algorithm*simulates the unitary evolution of a quantum system.

A quantum computer is an **analog machine** that uses a continuum of values and operates on the principle of probabilities. The result of a given algorithm is a sample from the probability distribution of the algorithm implementations plus possible errors. A quantum computer rarely gives the correct answer with 100% probability. Due to the very nature of such systems, the probability of an error largely depends on such factors as **decoherence**, for example. In simple words, it means that qubits interact with their environment in such a way that their quantum behavior deteriorates and eventually disappears.

## Where Quantum Computing Could Help?

**Quantum modeling of complex systems**. Quantum computing has the potential to enhance the precision and speed of complex simulations dramatically. For example, modeling weather, where you can simulate large-scale atmospheric systems' behavior, can provide more accurate predictions, improving disaster preparedness and resource allocation. Other examples include solving the quantum three-body problem and analyzing social dynamics.

**Quantum chemistry and pharmacology**. Here, we speak of calculating the properties of molecules without the need for their synthesis and modeling chemical reactions without the need to start them. It can expedite the discovery of new materials and drugs, potentially revolutionizing pharmaceutical development and leading to more effective treatments for various diseases.

**Logistics**. Quantum algorithms can optimize supply chain management, route planning, searching for the shortest routes (traveling salesman problem), and resource allocation, leading to cost reductions and improved efficiency. It is crucial for industries involved in shipping, e-commerce, and large-scale distribution networks.

Read Also Top 5 Supply Chain Management Software That Streamline and Upgrade Your Business Processes

**Quantum metrology**. Quantum computing can enhance measurement precision, making it invaluable in metrology. They can improve the accuracy of timekeeping, GPS tracking, and the calibration of scientific instruments, which can help improve navigation, telecommunications, and fundamental research.

**Quantum machine learning**. Modeling neural networks (both artificial and biological), processing and structuring big data using a quantum version of the principal component method (QPCA), searching for anomalies, protecting against fraud, and compiling algorithms for recommendation systems.

**Materials science**. Quantum computers can accelerate the discovery of new materials with desired properties. This tech has applications in fields such as renewable energy, where developing more efficient solar cells and batteries is crucial.

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**Finance**. With unprecedented speed, Quantum computing can solve complex financial modeling and optimization problems, such as portfolio optimization, risk assessment, and option pricing. It can lead to more informed investment decisions and improved risk management.

**Quantum cryptography**. While quantum computers have the potential to break existing encryption schemes (RSA and ECC) with Shor's algorithm, they can also provide new cryptographic techniques based on quantum principles, like quantum key distribution (QKD). It can enhance the security of communication systems and protect sensitive data.

## Are There Real Quantum Computers? Can I Buy One? Can It Run Minecraft?

Yes, No, and No.

For example, the most powerful of the existing quantum computers currently is the IBM Osprey, with 433 physical qubits launched in November 2022. More humble models also exist. Spin-2 manufactured by QuTech at TU Delft has only 2 qubits.

However, replacing your laptop or smartphone with a quantum computing device is not going to happen in the foreseeable future. The thing is that such systems require special conditions to operate correctly. The state of coherent superposition, one of the quantum computing cornerstones, requires complete isolation of qubits from the outside world. Also, ultra-low temperature is required.

The more qubits you have, the more difficult it is to keep them in superposition. The main obstacle here is the decoherence that we discussed earlier. Particles tend to become entangled with the environment and transmit information to the outside world. Today, quantum systems operate in laboratories equipped with sophisticated tools or specially designed refrigerators. Their appearance is also far from our idea of what an average computer looks like. For example, Google's Sycamore looks like a sci-fi chandelier concept:

*Source: NewScientist*

This bad boy has performed in 200 seconds a calculation that would have taken a classical supercomputer 10 thousand years to complete. Later, IBM disputed this result, saying the Summit supercomputer could do it in 2.5 days.

How you program when dealing with quantum computing also differs from the classic systems. A program on a quantum computer is a real experiment. The qubits of a quantum computer have classical values (0 or 1) at the input and output, but everything that happens in between actually occurs in a black box. Superposition cannot be directly observed or directly measured. When you measure a qubit, its superposition always goes into one of two classical states: 0 or 1. But with the help of magnetic pulses, you can indirectly change the probability ratio while the qubit is in superposition without measuring it.

If there are many qubits, their probabilities can be entangled with each other so that the system produces one of the results with a higher total probability than the others. The essence of quantum programming comes down to building a network of entangled qubits so that at the output, one of the circuits gives the maximum result (more ones), and all the others give the minimum result (more zeros). To do this, you need to build an interference system in which the paths leading to incorrect answers interfere destructively and are canceled, and those leading to the correct ones are strengthened.

In other words, simply downloading and installing Firefox on a quantum computer to surf the quantum Internet won't work. A quantum computer most probably will never completely replace a classical one. It is practically useless for most calculations that a regular computer can perform. But it is effective when you must sort through many options and choose the right one.

## Conclusions

Quantum computers are the future of technology, the taste of which we can feel today. Due to its intricate nature, quantum computing will probably exist only in laboratory-like environments for a long time. However, the computational possibilities it opens could impact our lives sooner than we thought. They can help pharmaceutical companies cure diseases more efficiently and open new opportunities to design new materials. In any case, it is better to prepare in advance and ensure you will be 100% ready when quantum computing becomes available to everyone. A worthy solution would be to begin long-term relationships with reliable software developers today so that you have a time-tested partner for work in the quantum era.