Quantum technology is set to revolutionize IT and drive advancements in many other fields. We explain the key concepts surrounding quantum computers.
Quantum computing takes advantage of the nearly mystical phenomena of quantum mechanics to make, at least in theory, huge leaps in computational power. These machines are expected to surpass even the most powerful supercomputers of today and tomorrow.
However, they won’t replace traditional computers anytime soon. For many applications, classical computers will remain the simplest and most cost-effective solution. Still, quantum computers hold exciting potential for breakthroughs in various fields, from materials science to drug discovery. Companies have been experimenting with these machines for years, aiming to develop lighter, more powerful batteries for electric vehicles or discover new drugs. The secret to quantum computing’s power lies in its ability to create and manipulate quantum bits, or qubits.
1. What is a qubit?
Today’s computers use bits, which are electrical or optical pulses representing either 1 (on) or 0 (off). Everything digital, from tweets and emails to songs on iTunes and YouTube videos, consists of long strings of these binary digits.
Quantum computers, on the other hand, use qubits. These are “states” of subatomic particles like electrons or photons. In quantum physics, when scientists say a quantum system is in a specific state, they mean it has a particular energy, is located in a specific place, or moves at a certain speed.
Generating and controlling qubits is a significant scientific and technical challenge. Companies like IBM, Google, and Rigetti Computing use superconducting circuits, cooled to temperatures colder than space. Others, like Ionq, trap individual charged atoms in electromagnetic fields on a silicon chip inside ultra-high vacuum chambers. In both cases, the goal is to isolate qubits in a controlled quantum state.
Qubits possess some quantum properties that, at first glance, seem inexplicable. This allows a group of qubits to deliver far more computational power than an equivalent number of binary bits. One such property is called superposition, and another is entanglement.
2. What is superposition?
Qubits can represent many possible combinations of 1 and 0 simultaneously. This ability to exist in multiple states at once is called superposition. Researchers use precise lasers or microwave beams to manipulate qubits into this state.
Thanks to this counterintuitive phenomenon, a quantum computer with several qubits in superposition can process a large number of possible outcomes simultaneously. The final result of a calculation only materializes when the qubits are measured, at which point their quantum state “collapses” into either 1 or 0.
3. What is entanglement?
Scientists can create pairs of qubits that are “entangled,” meaning both are linked in a single quantum state. When the state of one qubit changes, the state of the other changes instantly, even across vast distances.
No one fully understands how or why quantum entanglement works, not even Einstein, who once referred to it as “spooky action at a distance.” However, it is key to the power of quantum computers. In a traditional computer, doubling the number of bits roughly doubles its processing power. In a quantum computer, adding more qubits exponentially increases its processing power thanks to entanglement.
This enables quantum computers to perform calculations much faster with specially designed quantum algorithms. However, quantum computers are still highly prone to errors due to a phenomenon known as decoherence.
4. What is decoherence?
Decoherence happens when qubits interact with their environment in a way that causes their quantum behavior to “decay” and eventually vanish. The quantum state is extremely sensitive, and the slightest vibration or temperature change—called “noise” in quantum terms—can knock them out of superposition before they’ve finished their work. That’s why researchers go to great lengths to protect qubits in cooled, vacuum-sealed chambers.
Even with these precautions, quantum noise still causes many errors. Smart quantum algorithms can correct some of these, and adding more qubits helps. However, thousands of standard qubits will likely be needed to create a single reliable “logical” qubit, which will consume a large portion of the computer’s capacity.
Companies like IBM have been pushing the boundaries with more qubits. IBM introduced the Eagle system in 2021 with a then-record 127 qubits. In November 2022, they unveiled the Osprey processor with 433 qubits, followed by the Condor processor with 1,121 qubits in December 2023. But a startup called Atom Computing surpassed these milestones by releasing a quantum computer with 1,180 qubits in October 2023.
Modular quantum computers, which link multiple processors together, are also emerging as a trend. IBM’s Heron chip, launched in 2023, has only 133 qubits but is five times more powerful than the 127-qubit Eagle. These high-quality qubits have led IBM to project the ability to perform up to 5,000 qubit operations in a row without significant issues by 2024. The ultimate goal is quantum supremacy.
5. What is quantum supremacy?
Quantum supremacy is the point when a quantum computer can perform a mathematical calculation that no classical supercomputer could accomplish in a reasonable timeframe.
It remains unclear how many qubits are needed to achieve this, as researchers continue developing new algorithms to boost classical computers’ performance, and supercomputers are becoming increasingly powerful. However, the race to reach this milestone is in full swing, with researchers testing their machines against the world’s best supercomputers.
Even without officially declaring quantum supremacy, companies are already using quantum computers for real-world applications. IBM, Rigetti, and D-Wave, a Canadian company, are making quantum systems available, while Chinese firms like Alibaba are also entering the market. Some companies purchase their own quantum computers, while others access them through cloud services.
6. Where will quantum computers be most useful first?
One of the most promising uses of quantum computers is simulating molecular behavior at the atomic level. Automakers like Volkswagen and Daimler use quantum computers to simulate the chemical composition of electric vehicle batteries, aiming to enhance their performance. Pharmaceutical companies also use quantum systems to analyze and compare compounds that could lead to new drugs.
Quantum computers are also excellent for solving optimization problems, rapidly testing numerous solutions. For instance, Airbus uses them to calculate the most fuel-efficient flight paths, and Volkswagen has introduced a service to optimize bus and taxi routes in cities, reducing congestion. Some researchers believe quantum computers could also accelerate advancements in artificial intelligence.
It may take several more years for quantum computers to reach their full potential. Universities and companies working on them face a shortage of qualified researchers and, at times, a lack of suppliers for critical components. But once these exotic machines deliver on their promise, they could revolutionize industries and spark innovation across the globe.
Author of this article: Martin Giles, Senior Industry Fellow at the Center for Digital Transformation, University of California, Irvine.