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\n Media contact:<\/strong> Kayla Albert, 765-494-2432, wiles5@purdue.edu<\/a> <\/p>\n <\/div>\n
\u201cSingle photons are the building blocks of quantum photonics. The biggest challenges in scaling up a quantum photonic integrated circuit have to do with creating good single-photon sources,\u201d said Vladimir Shalaev<\/a>, the Bob and Anne Burnett Distinguished Professor in Electrical and Computer Engineering.<\/p>\n\n\n\n Shalaev and Alexandra Boltasseva<\/a> lead work in Purdue\u2019s Elmore Family School of Electrical and Computer Engineering<\/a>, Birck Nanotechnology Center<\/a>, and the Purdue Quantum Science and Engineering Institute<\/a> on key challenges with building quantum photonic integrated circuits. Their past discoveries on how to manipulate light on the nanoscale have been foundational to the fields of photonics and optics. For multiple years<\/a>, they have each been recognized on the Clarivate Highly Cited Researchers list for work ranking in the top 1% of citations in the Web of Science.<\/p>\n\n\n\n Boltasseva, the Ron and Dotty Garvin Tonjes Distinguished Professor in Electrical and Computer Engineering, also was featured on last year\u2019s Quantum 100 list<\/a> as part of the United Nations-designated International Year of Quantum Science and Technology.<\/p>\n\n\n\n One of the difficulties with building a quantum photonic integrated circuit is generating one photon at a time to take the form of a qubit.<\/p>\n\n\n\n In 2021, Shalaev and Boltasseva published a study in Science Advances<\/a> demonstrating a way to emit single photons using silicon nitride, a material that has become the industry standard for constructing quantum photonic platforms.<\/p>\n\n\n\n But the process the industry has been using for photon emission, called spontaneous parametric down-conversion, generates single photons inconsistently and with low efficiency.<\/p>\n\n\n\n The method Shalaev and Boltasseva\u2019s team developed emits exactly one photon at room temperature from dozens of locations on a silicon nitride platform every time a laser beam shoots through it.<\/p>\n\n\n\n The sources of photon emission are modifications to atomic structure, called \u201cdefects,\u201d that the researchers created within the platform. These atomic defects limit light emission to a single photon at a time.<\/p>\n\n\n\n Shalaev and Boltasseva have also since shown in a study presented at the 2022 Conference on Lasers and Electro-Optics<\/a> that they can control the placement and number of defects by embedding them in nanosized pillars on the silicon nitride platform, which would allow the platform to be manufactured more uniformly for use in a quantum photonic integrated circuit.<\/p>\n\n\n\n Another issue Shalaev and Boltasseva are tackling is that single photons don\u2019t readily interact with each other, making them hard to control on a chip using switches.<\/p>\n\n\n\n In a conventional computer, switches called transistors toggle bits between zero and one states to process information. Similarly, switches in a quantum photonic integrated circuit would enable photons to act as qubits.<\/p>\n\n\n\n Shalaev and Boltasseva\u2019s research team reported in a Nature Nanotechnology paper<\/a> last year that they built a switch<\/a> capable of operating on the level of single photons.<\/p>\n\n\n\n The proof-of-concept switch adapts a mechanism that the industry has used to modulate light with another high-intensity light beam for applications such as fiber-optic communications. This mechanism, called optical nonlinearity, allows a \u201ccontrol\u201d light beam to interact with a \u201cprobe\u201d beam but at power levels that would be too high to work with single photons.<\/p>\n\n\n\n With the Purdue-developed method, a single photon from the control beam strikes silicon, creating an electron that then triggers an avalanche of electrons. This avalanche alters how light passes through a material, which also changes refractive index, a property that controls light propagation. By changing silicon\u2019s refractive index, the probe beam passes through the device only when a single photon starts the electron avalanche process, effectively allowing the photon to switch the beam on and off.<\/p>\n\n\n\n Even though qubits based on photons would be less affected by their surroundings, a single disturbance could still cause qubits to fall out of superposition or entanglement, creating errors in a quantum computer\u2019s calculations.<\/p>\n\n\n\n This kind of disturbance is called decoherence. Purdue electrical and computer engineering professor Alexander Kildishev and Purdue graduate student Pranshu Maan led a team that included Shalaev and Boltasseva in demonstrating an approach that could make it possible to prevent decoherence by anticipating it before it happens. The team published findings in Nature Communications<\/a> this year.<\/p>\n\n\n\n \u201cDecoherence is seemingly random, but in fact there is a certain pattern that can be recognized. This study takes an important step in identifying such a pattern using machine learning,\u201d Boltasseva said.<\/p>\n\n\n\n The team found through statistical-physics analysis that the way decoherence happens over time presents a pattern. They then used machine learning to validate that these patterns have information that could be predicted. The researchers turned these components into a framework that learns and could anticipate the dynamics of a quantum system, which would then enable proactive control of decoherence rather than only responding to it after it occurs.<\/p>\n\n\n\n With this framework, the researchers demonstrated a way to predict and reduce one of the major causes of decoherence, called spectral diffusion. This phenomenon happens when an emitted photon shifts across the electromagnetic spectrum due to disorder that naturally happens in the surrounding environment, changing the photon\u2019s frequency and therefore its energy level. Because superposition only works if all photons in a quantum system are indistinguishable from one another, a change in a single photon\u2019s energy level would cause superposition to fall apart.<\/p>\n\n\n\n The researchers discovered that spectral shifts retain a memory of how an emitted photon\u2019s frequency has wandered over time, revealing a predictable temporal pattern. The team developed an algorithm with a built-in memory mechanism and trained it on data from individual quantum emitters to predict future spectral shifts. Using these predictions, they showed that an anticipatory-control approach could reduce spectral shifts by as much as 20-fold in the quantum systems studied.<\/p>\n\n\n\n Just being able to predict decoherence could have a big impact on a quantum computer\u2019s performance.<\/p>\n\n\n\n \u201cYou can\u2019t get rid of decoherence \u2014 it\u2019s the law of nature that everything fluctuates. But if you recognize the pattern of decoherence and learn how to control it, then you can minimize it,\u201d Shalaev said. \u201cLet\u2019s say you need a hundred qubits to run a quantum algorithm, but typically far more than that, say 10,000 qubits, to deal with errors caused by decoherence. If I minimize those errors somehow, then the number of qubits needed to run my algorithm would also be minimized.\u201d<\/p>\n\n\n\n In principle, this approach could lay the foundation for making it possible to anticipate decoherence across multiple quantum systems, which is needed for building the scalable quantum architecture that quantum computers would use. Those predictions could then be combined with active tuning to keep different emitters more closely aligned, improving the indistinguishability and synchronization of the photons they generate.<\/p>\n\n\n\n Next, the team plans to use tools from statistical physics to extract the hidden properties of a quantum system\u2019s fluctuating environment from its measured dynamics. These physical insights will be incorporated into machine-learning models to improve their ability to predict decoherence. The team will also investigate whether the models can identify the microscopic processes responsible for spectral shifts, with the long-term goal of predicting and suppressing decoherence before it significantly disrupts the quantum state.<\/p>\n\n\n\n Shalaev and Boltasseva\u2019s work related to quantum photonic integrated circuits is based on multiple technologies disclosed to the\u00a0Purdue Innovates Office of Technology Commercialization<\/a>, which applied for patents to protect the intellectual property<\/a>. The researchers\u2019 work on the single-photon emitter and the algorithm for predicting decoherence was supported by the U.S. Department of Energy\u2019s (DOE) Quantum Science Center, a National Quantum Information Science Research Center under the DOE\u2019s Office of Science. The algorithm\u2019s development also received support from the Purdue-led Quantum Photonic Integrated Design Center<\/a>, an Energy Frontier Research Center funded by DOE\u2019s Office of Science through the Basic Energy Sciences program (award number DE-SC0025620). The team\u2019s work on the single-photon switch was funded by the U.S. Army Research Laboratory\u2019s Army Contracting Command \u2014 Aberdeen Proving Ground, Research Triangle Park division (grant number W911NF-25-2-0060).<\/p>\n\n\n\n This research exemplifies Purdue\u2019s growing leadership in quantum science and engineering and is a part of Purdue Computes<\/a>, a comprehensive initiative that spans computing departments, physical artificial intelligence, quantum science and semiconductor innovation. Through a partnership between the colleges of Science and Engineering, Purdue has launched an expanded portfolio of quantum degree programs spanning certificates, minors, master\u2019s degrees and doctoral concentrations. Students have opportunities to learn alongside faculty pushing the frontiers of quantum science, engineering and technology, creating a direct connection between groundbreaking research and the workforce needed to advance the emerging quantum economy.<\/p>\n\n\n\n Purdue University is a research institution ranked among the top 10 public universities in the United States. More than 111,000 students study at Purdue across multiple campuses, including more than 57,000 at our main campus locations in West Lafayette and Indianapolis. As a land-grant university committed to affordability and accessibility, Purdue\u2019s main campus has frozen tuition 14 years in a row, enabling more students than ever to graduate debt-free.<\/p>\n\n\n\n Room-temperature single-photon emitters in silicon nitride<\/em> Large scale deterministic creation of single photon emitters in silicon nitride nanopillars<\/em> All-optical modulation with single photons using an electron avalanche<\/em> Anticipating decoherence in quantum systems<\/em>![\"Purdue](\"https:\/\/www.purdue.edu\/newsroom\/wp-content\/uploads\/2026\/11\/shalaev-lab.jpg\" "\\"\\"")
A more reliable way to produce single photons<\/h2>\n\n\n\n
A single-photon switch<\/h2>\n\n\n\n
![\"An](\"https:\/\/www.purdue.edu\/newsroom\/wp-content\/uploads\/2026\/11\/quantum-lab.jpg\" "\\"\\"")
A tool for predicting quantum decoherence<\/h2>\n\n\n\n
About Purdue University<\/h2>\n\n\n\n
Papers<\/h2>\n\n\n\n
Science Advances
DOI: 10.1126\/sciadv.abj0627<\/a><\/p>\n\n\n\n
2022 Conference on Lasers and Electro-Optics
Paper is available on the conference website<\/a>.<\/p>\n\n\n\n
Nature Nanotechnology
DOI: 10.1038\/s41565-025-02056-2<\/a><\/p>\n\n\n\n
Nature Communications
DOI: 10.1038\/s41467-026-72829-3<\/a><\/p>\n\n\n\n