New ‘fingerprint’ technique could catch faulty quantum hardware before it gets deployed - Interesting Engineering

A representational image.Krongkaew/Getty Images Quantum computing has long carried a paradox at its core: if a quantum computer eventually solves problems too difficult for any classical machine, how will anyone know whether its answer is correct? The challenge goes beyond checking the final result. Researchers also need to know whether the quantum hardware itself is doing what it claims to do. “Quantum computers present a fundamentally different challenge. Since they are expected to solve problems that are beyond the reach of classical computers, there may be no efficient classical method to benchmark them,” Shubhayan Sarkar, a postdoctoral researcher at the University of Gdansk, told Phys.org. Now, a new study by Shubhayan Sarkar, a postdoctoral researcher at the University of Gdansk, proposes a way to verify one of the most important building blocks of a quantum computer—its quantum gates—without relying on detailed knowledge of the machine’s internal design. The work addresses a problem that has remained largely unsolved in the field and could eventually make future quantum processors far more trustworthy. Turning quantum verification into a network problem Sarkar’s solution builds on earlier research showing that quantum states and measurements can be self-tested using a phenomenon known as quantum nonlocality. Nonlocality, whose experimental verification helped earn the 2022 Nobel Prize in Physics, allows distant quantum systems to produce correlations that cannot be explained by classical physics alone. By analyzing these correlations, researchers can certify that a system is genuinely quantum without opening it up and inspecting its hardware.More from ScienceSee AllScienceUS scientists find new material that outperforms copper in tiny computer chipsScienceCandy-inspired method yields first cold radium molecules for quantum experimentsScienceChina: Quantum teleportation proves nearly 3x more efficient at transmitting qubitsInterviewsThe plastics designed to last forever may finally have an off switchEnergySingle-reactor process yields 90% pure hydrogen fuel from mixed plastic waste In previous work, Sarkar and his colleagues developed a method capable of self-testing arbitrary quantum states and measurements. The new study extends that idea to quantum operations, specifically unitary gates. A unitary gate is a mathematical operation that manipulates quantum information while preserving it, making it the ideal representation of a quantum logic gate. As Sarkar explained, “since any quantum computer will be based on quantum chips that are basically unitary gates, self-testing unitary gates is certifying the ‘bricks’ of a quantum computer.” In short, verifying them is essential for proving that a quantum processor is functioning correctly. A star-shaped network to test quantum gates To achieve this, Sarkar designed a network-based certification scheme. Imagine a central server connected to several external nodes in a star-shaped arrangement. Between the server and each external node sits a quantum gate that can be switched on or off. When the gate is turned off, researchers first certify the external nodes and their quantum connections using specially designed Bell inequalities—mathematical tests that reveal whether the observed behavior can only be explained by quantum mechanics. Once these surrounding components are verified, the gate is switched back on. As the rest of the network has already been certified, researchers can use the resulting statistical patterns to determine whether the gate itself is operating correctly. More importantly, all of the data are collected within a single experiment and then analyzed together to certify every component. The study actually presents two versions of the protocol. The simpler version, called an “Almost Device-Independent” scheme, can in principle self-test any quantum unitary gate as long as the gate does not move quantum states outside their original mathematical subspace. This makes it significantly easier to implement while still avoiding detailed assumptions about the processor’s internal hardware. Every quantum operation leaves a unique fingerprint The researchers also developed a fully device-independent version of the protocol. This approach is more rigorous but also more demanding, as it requires additional quantum teleportation links within the network. These links must themselves be certified using further Bell tests before the gate-verification process can proceed. What makes the work particularly important is the theoretical result supporting both schemes. Sarkar proved that every quantum operation is associated with a unique set of observable correlations. In simple terms, each quantum gate leaves behind its own distinctive statistical fingerprint. By examining the correlations produced during an experiment, scientists can determine whether a specific gate—and no other—generated the observed behavior, apart from a small number of unavoidable ambiguities that cannot be eliminated experimentally. This capability could be especially valuable for developing countries and organizations that lack the resources or infrastructure to manufacture advanced quantum processors domestically. As quantum technologies become more widely available, many may need to import quantum chips from foreign suppliers and integrate them into their own computing platforms. Instead of relying solely on manufacturers’ claims, they could use certification methods like this one to independently verify that the imported hardware is performing exactly as intended. Building trust in the quantum era The work remains a proof-of-principle rather than a technology ready for deployment. Although small star-shaped quantum networks have already been demonstrated experimentally, the complete certification protocol described in the study has not yet been tested on real quantum processors. The method also relies on multiple Bell tests and assumptions about independent quantum sources, which could make large-scale implementation challenging. Still, the implications are significant. As governments and technology companies invest billions of dollars in quantum computing, concerns about verification, transparency, and reliability are becoming increasingly important. The recent debate surrounding claims about Microsoft’s Majorana-based quantum technology highlighted how difficult it can be for outsiders to independently assess the performance of emerging quantum hardware. A robust certification framework could provide an objective way to evaluate such claims. Sarkar’s next goal is to make the protocol more practical by reducing the number of Bell tests required and ensuring that it remains reliable even when real-world noise and imperfections are present. He also hopes to adapt the approach for publicly accessible quantum computing platforms such as those offered by IBM Quantum. If successful, users could one day verify the operations performed by a quantum computer without having to trust the company running it. “This would not just benchmark the quantum computing of these companies but also increase the trust of the general public in quantum computing,” Sarkar concluded. The study is published in the journal Physical Review Letters. Recommended ArticlesGet the latest in engineering, tech, space & science - delivered daily to your inbox.Sign up for freeBy subscribing, you agree to our Terms of Use and PoliciesYou may unsubscribe at any time.0COMMENTSubscribe toToday!Access to exclusive content, expert insights and a deeper dive into engineering and tech. No ads, no limits.Explore Now!ByRupendra BrahambhattRupendra Brahambhatt is an experienced writer, researcher, journalist, and filmmaker. With a B.Sc (Hons.) in Science and PGJMC in Mass Communications, he has been actively working with some of the most innovative brands, news agencies, digital magazines, documentary filmmakers, and nonprofits from different parts of the globe. As an author, he works with a vision to bring forward the right information and encourage a constructive mindset among the masses.TRENDINGLATEST1US firm gets permission for 600 MWh Minnesota battery project that can support electrical grid2Nuclear-powered ship design with dual molten salt reactors wins approval from US body3Flowing zinc battery retains 81% capacity after 5,500 cycles in durability tests4Los Alamos tests NVIDIA Vera CPUs for supercomputers targeting 12x faster performance5World-class nuclear fuel facility that can power next-gen reactors to be built with new fundingA representational image.Krongkaew/Getty Images Quantum computing has long carried a paradox at its core: if a quantum computer eventually solves problems too difficult for any classical machine, how will anyone know whether its answer is correct? The challenge goes beyond checking the final result. Researchers also need to know whether the quantum hardware itself is doing what it claims to do. “Quantum computers present a fundamentally different challenge. Since they are expected to solve problems that are beyond the reach of classical computers, there may be no efficient classical method to benchmark them,” Shubhayan Sarkar, a postdoctoral researcher at the University of Gdansk, told Phys.org. Now, a new study by Shubhayan Sarkar, a postdoctoral researcher at the University of Gdansk, proposes a way to verify one of the most important building blocks of a quantum computer—its quantum gates—without relying on detailed knowledge of the machine’s internal design. The work addresses a problem that has remained largely unsolved in the field and could eventually make future quantum processors far more trustworthy. Turning quantum verification into a network problem Sarkar’s solution builds on earlier research showing that quantum states and measurements can be self-tested using a phenomenon known as quantum nonlocality. Nonlocality, whose experimental verification helped earn the 2022 Nobel Prize in Physics, allows distant quantum systems to produce correlations that cannot be explained by classical physics alone. By analyzing these correlations, researchers can certify that a system is genuinely quantum without opening it up and inspecting its hardware.More from ScienceSee AllScienceUS scientists find new material that outperforms copper in tiny computer chipsScienceCandy-inspired method yields first cold radium molecules for quantum experimentsScienceChina: Quantum teleportation proves nearly 3x more efficient at transmitting qubitsInterviewsThe plastics designed to last forever may finally have an off switchEnergySingle-reactor process yields 90% pure hydrogen fuel from mixed plastic waste In previous work, Sarkar and his colleagues developed a method capable of self-testing arbitrary quantum states and measurements. The new study extends that idea to quantum operations, specifically unitary gates. A unitary gate is a mathematical operation that manipulates quantum information while preserving it, making it the ideal representation of a quantum logic gate. As Sarkar explained, “since any quantum computer will be based on quantum chips that are basically unitary gates, self-testing unitary gates is certifying the ‘bricks’ of a quantum computer.” In short, verifying them is essential for proving that a quantum processor is functioning correctly. A star-shaped network to test quantum gates To achieve this, Sarkar designed a network-based certification scheme. Imagine a central server connected to several external nodes in a star-shaped arrangement. Between the server and each external node sits a quantum gate that can be switched on or off. When the gate is turned off, researchers first certify the external nodes and their quantum connections using specially designed Bell inequalities—mathematical tests that reveal whether the observed behavior can only be explained by quantum mechanics. Once these surrounding components are verified, the gate is switched back on. As the rest of the network has already been certified, researchers can use the resulting statistical patterns to determine whether the gate itself is operating correctly. More importantly, all of the data are collected within a single experiment and then analyzed together to certify every component. The study actually presents two versions of the protocol. The simpler version, called an “Almost Device-Independent” scheme, can in principle self-test any quantum unitary gate as long as the gate does not move quantum states outside their original mathematical subspace. This makes it significantly easier to implement while still avoiding detailed assumptions about the processor’s internal hardware. Every quantum operation leaves a unique fingerprint The researchers also developed a fully device-independent version of the protocol. This approach is more rigorous but also more demanding, as it requires additional quantum teleportation links within the network. These links must themselves be certified using further Bell tests before the gate-verification process can proceed. What makes the work particularly important is the theoretical result supporting both schemes. Sarkar proved that every quantum operation is associated with a unique set of observable correlations. In simple terms, each quantum gate leaves behind its own distinctive statistical fingerprint. By examining the correlations produced during an experiment, scientists can determine whether a specific gate—and no other—generated the observed behavior, apart from a small number of unavoidable ambiguities that cannot be eliminated experimentally. This capability could be especially valuable for developing countries and organizations that lack the resources or infrastructure to manufacture advanced quantum processors domestically. As quantum technologies become more widely available, many may need to import quantum chips from foreign suppliers and integrate them into their own computing platforms. Instead of relying solely on manufacturers’ claims, they could use certification methods like this one to independently verify that the imported hardware is performing exactly as intended. Building trust in the quantum era The work remains a proof-of-principle rather than a technology ready for deployment. Although small star-shaped quantum networks have already been demonstrated experimentally, the complete certification protocol described in the study has not yet been tested on real quantum processors. The method also relies on multiple Bell tests and assumptions about independent quantum sources, which could make large-scale implementation challenging. Still, the implications are significant. As governments and technology companies invest billions of dollars in quantum computing, concerns about verification, transparency, and reliability are becoming increasingly important. The recent debate surrounding claims about Microsoft’s Majorana-based quantum technology highlighted how difficult it can be for outsiders to independently assess the performance of emerging quantum hardware. A robust certification framework could provide an objective way to evaluate such claims. Sarkar’s next goal is to make the protocol more practical by reducing the number of Bell tests required and ensuring that it remains reliable even when real-world noise and imperfections are present. He also hopes to adapt the approach for publicly accessible quantum computing platforms such as those offered by IBM Quantum. If successful, users could one day verify the operations performed by a quantum computer without having to trust the company running it. “This would not just benchmark the quantum computing of these companies but also increase the trust of the general public in quantum computing,” Sarkar concluded. The study is published in the journal Physical Review Letters. Recommended ArticlesGet the latest in engineering, tech, space & science - delivered daily to your inbox.Sign up for freeBy subscribing, you agree to our Terms of Use and PoliciesYou may unsubscribe at any time.0COMMENTSubscribe toToday!Access to exclusive content, expert insights and a deeper dive into engineering and tech. No ads, no limits.Explore Now!ByRupendra BrahambhattRupendra Brahambhatt is an experienced writer, researcher, journalist, and filmmaker. With a B.Sc (Hons.) in Science and PGJMC in Mass Communications, he has been actively working with some of the most innovative brands, news agencies, digital magazines, documentary filmmakers, and nonprofits from different parts of the globe. As an author, he works with a vision to bring forward the right information and encourage a constructive mindset among the masses.TRENDINGLATEST1US firm gets permission for 600 MWh Minnesota battery project that can support electrical grid2Nuclear-powered ship design with dual molten salt reactors wins approval from US body3Flowing zinc battery retains 81% capacity after 5,500 cycles in durability tests4Los Alamos tests NVIDIA Vera CPUs for supercomputers targeting 12x faster performance5World-class nuclear fuel facility that can power next-gen reactors to be built with new funding