The concept of quantum computing is already incredibly complex, but one of the most basic questions surrounding it has recently been answered. Graduate student Urmila Mahadev has answered the seemingly simple question of how to tell that a quantum computer has actually done what is has been told. Has it accomplished the tasks given to it? How exactly has it accomplished this? These questions have been a puzzle since the technology’s inception and Mahadev has spent years solving it.

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Quantum computers are complicated pieces of technology but I will attempt to explain. Your typical computer only has so much processing power, meaning that it can accomplish so many tasks, namely strings of numbers, in a given period of time. Researchers needed the computation power of a vast number of computers working collectively to process and store temporary data for things like searching the universe for new planets. This would be nearly impossible to accomplish in any reasonable timeframe without such processing power to take in the number of objects seen in space. Companies that make planes also use these quantum computers to run tests with such labor intensive software. These feats are possible due to the actual capabilities of such a device. It was designed using principles of quantum physics which has allowed for the storage of information on subatomic particles which is far more efficient that traditional methods. The storage units are known as qubits which typically express answers stored in binary. The issue, however is that when dealing with subatomic particles, an issue known as superposition arises. This is the idea that a quantum system can be in multiple measurable states at the same time, deviating from fundamental physical properties. This brought about an issue for researchers as they could not realistically measure the current state of the processes within a quantum computer to ensure it was accomplishing a given task correctly. The trick, it would seem, is to keep the end goal of the computation a “secret” from the computer which is where Mahadev’s work comes in.

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The concept that she has come up with is a cryptography protocol which is not necessarily new. It is actually the tool that allows us as users of cloud storage systems, to securely share our data with those servers. It essentially alters the information that you’re inputting so that it is only received in part, without a final goal in mind for the computer. It is then sent back to you, post computation without the cloud service actually knowing what it has accomplished. In the case of quantum computing, this was far more difficult. One goal was to have the computer output random numbers and the researchers were to prove that they were truly random, justifying the computers capabilities. Mahadev managed to create a “trapdoor” function that enabled the user to verify the quantum computers proof of accurate completion for a computation. She accomplished this with other researchers and their findings were successful in practice. To prove the computer correct, you must “read” the qubits and check information but to do so, the verifier must use another smaller quantum machine to check the qubit for accuracy. These two machines cannot communicate because of superposition. This state causes any measurement being taken to change the readings of the quantum computer, meaning that an accurate read would be impossible. The second quantum device circumvents this by gathering one output for every two inputs within the larger computer. This allows for accurate measurements, thus giving the researchers the ability to prove their technology is giving them real answers.

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Urmila Mahadev has answered a vital question for the emerging technology that is quantum computing. As she has said herself, she is eager to find and solve her next puzzle. However, finding the solution to such a complex problem will inevitable only lead to more questions and curious, dedicated researchers like Mahadev will surely continue finding solutions.