## A Computing Revolution: A Step Towards Realizing Quantum Computing

**By Bryan Lee**

In the decades following the invention of the first electronic digital computer (the Atanasoff-Berry computer) in 1942, the augmented rate of computation allowed by the developments in computers, such as increased processor speed, has improved the potential impact humans can make in nearly every field imaginable from sequencing the human genome to landing NASA’s Mars rovers. However, another computing revolution may be dawning.

Quantum computers—a relatively new theoretical type of computer—have the potential to significantly increase the rate of computation over classical computers, the computers we currently use. Specifically, classical computers perform computations by changing the value of their many bits (the smallest unit of data in a computer) which exist in either of the two states: “0” or “1”. However, quantum computers utilize quantum bits, or “qubits”, for computation. These qubits exist in a state called a “superposition” in which both the “0” and “1” states can exist simultaneously. The existence of superpositions is primarily what gives quantum computers the potential to compute at a much faster rate than classical computers.

For example, there are four possible combinations of two bits: 00, 01, 10, and 11. As these states exist independently of one another, a classical computer must conduct four separate operations (i.e. switching the values of pairs of bits) to change all of the states, one for each state. However, quantum computers can perform certain tasks using only a fraction of the operations used by classical computers. In quantum computers, although two qubits are also required to represent all four possible combinations of two bits, only two operations are necessary (one for each qubit) because each qubit operation effectively acts on both the “0” and “1” states at the same time rather than in sequence. As each qubit can operate on the “0” and “1” states simultaneously, operations are required to act upon all combinations of n binary values using n qubits, one operation for each bit. However, two operations are necessary for each bit when using classical bits, requiring 2n total operations. Consequently, quantum computers can conduct computations on considerably more states than classical computers with an equal number of operations, substantially accelerating the rate of computation. For example, this means that operating on all possible combinations of 10 binary values (i.e. 210=1024 possible states) using 10 qubits is approximately 100 times faster than when using 10 classical bits (i.e. 1024/10≈100).

However, one significant limitation of quantum computing is that qubits in their current form are very sensitive to environmental fluctuations, such as variation in the surrounding temperature and interaction with other particles (such as electrons). This can cause a qubit system to accumulate errors and output an incorrect result, a phenomenon termed quantum decoherence.

In order to reduce the effects of quantum decoherence (a process known as fault-tolerant quantum computing) researchers at the University of Pennsylvania, Johns Hopkins University, and Goucher College investigated the development of superconducting topological insulators (STIs)—materials that behave like insulators on their interior and superconductors (i.e. materials which conduct electricity with no electrical resistance) on their exterior.

Although these materials have previously been theorized to have the potential to create a fault-tolerant quantum computer, there are still two significant limitations: first, cracks typically form between the superconductor and the insulator which reduces electrical conductivity and diminishes the reduction of quantum decoherence. Second, very intricate printing methods are currently required to create STIs, typically using nanoscale rods called nanowires, increasing the cost of production and decreasing product scalability. The researchers looked to address both of these drawbacks by creating a new STI using the topological insulator bismuth selenide (Bi2Se3) with added regions of the element palladium (Pd). The palladium was then merged with the bismuth selenide by heating the palladium at 290°C and was slowly allowed to cool, a process termed thermal annealing. The added palladium impurities in bismuth selenide modify the topological insulator’s electrical properties which allows the STI to act like a superconductor. While previous methods of creating STIs characteristically required expensive machinery, this new process of thermal annealing is much cheaper because it requires a low-cost heating source. In addition, embedding the superconducting material (Pd) directly onto the topological insulator (Bi2Se3) significantly reduces the formation of cracks, improving fault-tolerance and decreasing quantum decoherence.

In the future, this advancement can allow for the development of more stable and scalable quantum computers. However, researchers recognize that there are still many steps to take before this new form of computation can be fully developed. Despite this, it is feasible that we will continue to see advancements in quantum computing for applications in areas such as increasing the accuracy of computer object detection and creating more expansive protein folding simulations, bringing us closer to a quantum computing revolution.

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