![]() The researchers found that imperfect clocks were not a problem for current quantum computers, given the limited number of qubits they possess. But we feel they will be the hardest to get rid of, resulting in a kind of fundamental limit on the achievable accuracy of a quantum computation due to imperfect timekeeping.” -Jake Xuereb, Vienna University of Technology “These errors are far from those impeding current quantum technologies the most. In the new study, the scientists explored how imperfect timekeeping might impact quantum algorithms made up of a series of quantum gates. Prior work found that timing errors could disrupt individual quantum gates. “What was unexplored was the theory of how the physics of timekeeping impacts quantum algorithms.” This matter “is definitely a question that had been explored by experimentalists building quantum computers,” Xuereb says. Given how real clocks are never perfect, the researchers explored the impact that imperfect timing would have on quantum computers. But this isn’t true-we only have knowledge of time with reference to some clock.” “Physicists seem to think it’s this parameter that they have full knowledge of and they can chuck into their equations for free. “Time is often taken for granted,” Xuereb says. ![]() Physics dictates that in the absence of having an infinite amount of energy available to it, a clock can never have both perfect resolution and perfect precision at the same moment, the scientists found. Its resolution describes the smallest piece of time a clock can measure, and its precision explains how much inaccuracy one can expect with each tick of the clock. ![]() The researchers note that every clock has two key properties-its resolution and its precision. “We only have knowledge of time with reference to some clock.” -Jake Xuereb, Vienna University of Technology Therefore, accurate timekeeping is critical. Whenever a quantum computer performs an operation, it has to expose its components to very specific forces for a very specific amount of time, explains study lead author Jake Xuereb, a quantum physicist at the Vienna University of Technology. The more components known as quantum bits, or qubits, that a quantum computer links together, the more basic computations known as quantum gates it can perform. Quantum computing can theoretically find answers to problems that classical computing would take eons to solve. Now it turns out that they may face a fundamental limit to large-scale performance-the imperfect nature of all clocks. The presented results are also relevant for quantum thermodynamics, as we demonstrate by introducing the class of Gibbs-preserving strictly incoherent operations, and solving the corresponding mixed-state conversion problem for a single qubit.The quantum computers that IBM, Google, Amazon, and others are developing face daunting challenges on the road to practical applications. For a single qubit, we show that the number of incoherent Kraus operators is not more than 5, and it remains an open question if this number can be reduced to 4. In this work, we contribute to such a characterization by proving several upper bounds on the maximum number of incoherent Kraus operators in a general incoherent operation. An important open problem in this context is a simple characterization for incoherent operations, constituted by all possible transformations allowed within the resource theory of coherence. The recently established resource theory of quantum coherence studies possible quantum technological applications of quantum coherence, and limitations which arise if one is lacking the ability to establish superpositions. Download a PDF of the paper titled Structure of the resource theory of quantum coherence, by Alexander Streltsov and 3 other authors Download PDF Abstract:Quantum coherence is an essential feature of quantum mechanics which is responsible for the departure between classical and quantum world.
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