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MIT researchers have designed a way to generate, at room temperature, more single photons for carrying quantum information. The design, they say, holds promise for the development of practical quantum computers.<\/p>\nNuevo dise\u00f1o de doble cavidad emite m\u00e1s fotones individuales que pueden transportar informaci\u00f3n cu\u00e1ntica a temperatura ambiente.<\/p>\n
MIT researchers have designed a way to generate, at room temperature, more single photons for carrying quantum information. The design, they say, holds promise for the development of practical quantum computers.<\/p>\n
Quantum emitters generate photons that can be detected one at a time. Consumer quantum computers and devices could potentially leverage certain properties of those photons as quantum bits (\u201cqubits\u201d) to execute computations. While classical computers process and store information in bits of either 0s or 1s, qubits can be 0 and 1 simultaneously. That means quantum computers could potentially solve problems that are intractable for classical computers.<\/p>\n
A key challenge, however, is producing single photons with identical quantum properties \u2014 known as \u201cindistinguishable\u201d photons. To improve the indistinguishability, emitters funnel light through an optical cavity where the photons bounce back and forth, a process that helps match their properties to the cavity. Generally, the longer photons stay in the cavity, the more they match.<\/p>\n
But there\u2019s also a tradeoff. In large cavities, quantum emitters generate photons spontaneously, resulting in only a small fraction of photons staying in the cavity, making the process inefficient. Smaller cavities extract higher percentages of photons, but the photons are lower quality, or \u201cdistinguishable.\u201d<\/p>\n
In a paper published today in\u00a0Physical Review Letters<\/em>, the researchers split one cavity into two, each with a designated task. A smaller cavity handles the efficient extraction of photons, while an attached large cavity stores them a bit longer to boost indistinguishability.<\/p>\n Compared to a single cavity, the researchers\u2019 coupled cavity generated photons with around 95 percent indistinguishability, compared to 80 percent indistinguishability, with around three times higher efficiency.<\/p>\n \u201cIn short, two is better than one,\u201d says first author Hyeongrak \u201cChuck\u201d Choi, a graduate student in the MIT Research Laboratory of Electronics (RLE). \u201cWhat we found is that in this architecture, we can separate the roles of the two cavities: The first cavity merely focuses on collecting photons for high efficiency, while the second focuses on indistinguishability in a single channel. One cavity playing both roles can\u2019t meet both metrics, but two cavities achieves both simultaneously.\u201d<\/p>\n Joining Choi on the paper are: Dirk Englund, an associate professor of electrical engineering and computer science, a researcher in RLE, and head of the Quantum Photonics Laboratory; Di Zhu, a graduate student in RLE; and Yoseob Yoon, a graduate student in the Department of Chemistry.<\/p>\n The relatively new quantum emitters, known as \u201csingle-photon emitters,\u201d are created by defects in otherwise pure materials, such as diamonds, doped carbon nanotubes, or quantum dots. Light produced from these \u201cartificial atoms\u201d is captured by a tiny optical cavity in photonic crystal \u2014\u00a0a nanostructure acting as a mirror. Some photons escape, but others bounce around the cavity, which forces the photons to have the same quantum properties \u2014 mainly, various frequency properties. When they\u2019re measured to match, they exit the cavity through a waveguide.<\/p>\n But single-photon emitters also experience tons of environmental noise, such as lattice vibrations or electric charge fluctuation, that produce different wavelength or phase. Photons with different properties cannot be \u201cinterfered,\u201d such that their waves overlap, resulting in interference patterns. That interference pattern is basically what a quantum computer observes and measures to do computational tasks.<\/p>\n Photon indistinguishability is a measure of photons\u2019 potential to interfere. In that way, it\u2019s a valuable metric to simulate their usage for practical quantum computing. \u201cEven before photon interference, with indistinguishability, we can specify the ability for the photons to interfere,\u201d Choi says. \u201cIf we know that ability, we can calculate what\u2019s going to happen if they are using it for quantum technologies, such as quantum computers, communications, or repeaters.\u201d<\/p>\n