Scientists have found a method to convert quantum information from one type of quantum technology to another. This development is significant as it has important applications in quantum computing, communication, and networking.
On Wednesday, the journal Nature published a study introducing a novel method for converting quantum information from the format utilized by quantum computers into the format required for quantum communication. The study details a breakthrough in photon manipulation that could enable the creation of more resilient quantum networks.
Quantum information technologies rely on photons for their ability to carry quantum information. However, photons can exist at different frequencies, and different technologies use them at different frequencies. Superconducting qubits, for instance, use photons that move at microwave frequencies to store quantum information. Unfortunately, microwave photons are not suitable for quantum networks or connecting quantum computers as they lack the ability to retain quantum information for long-distance communication.
“A lot of the technologies that we use for classical communication—cell phones, Wi-Fi, GPS and things like that—all use microwave frequencies of light,” said Aishwarya Kumar, a postdoc at the James Franck Institute at University of Chicago and lead author on the paper. “But you can’t do that for quantum communication because the quantum information you need is in a single photon. And at microwave frequencies, that information will get buried in thermal noise.”
One possible way to improve quantum communication is to use a higher-frequency photon, such as an optical photon, which can better protect the quantum information from ambient noise. However, directly transferring information from one photon to another is not feasible, so scientists have been looking for intermediary matter to facilitate the transfer. Although some experiments have used solid-state devices, the latest research by Aishwarya Kumar focuses on using atoms, which provide a more fundamental solution to the problem. By exploiting the specific energy levels of electrons in atoms, Kumar and her team have developed a new method to convert quantum information from the format used by quantum computers to the format needed for quantum communication.
The behavior of electrons in atoms is governed by the laws of quantum mechanics, which dictate that electrons can exist only in certain energy states, or energy levels. When an atom absorbs a photon that has just the right amount of energy, an electron in the atom can jump from a lower energy level to a higher one. Conversely, when an electron drops down from a higher energy level to a lower one, the atom emits a photon with energy equal to the energy difference between the two levels. This phenomenon is the basis for the technology developed in Kumar’s experiment, which aimed to transfer quantum information between photons of different frequencies by using atoms as intermediaries.
Kumar’s technology takes advantage of a unique feature of rubidium atoms, which have two gaps in their energy levels that align with the energies of both microwave and optical photons. By precisely manipulating the electrons within the atom using lasers, the technology enables the atom to absorb a microwave photon carrying quantum information, and subsequently emit an optical photon that also carries the same quantum information. This process of converting quantum information from one mode to another is referred to as “transduction.” Through this approach, the technology offers a novel way of transducing quantum information that could be crucial for building practical quantum communication systems.
Effectively using atoms for this purpose is made possible by the significant progress scientists have made in manipulating such small objects. “We as a community have built remarkable technology in the last 20 or 30 years that lets us control essentially everything about the atoms,” Kumar said. “So the experiment is very controlled and efficient.”
According to Kumar, the team’s success is due in part to recent advancements in the field of cavity quantum electrodynamics (QED). In this area of research, a photon is confined within a reflective, superconducting chamber, which enhances the interaction between the photon and any matter placed inside. By using this technique to trap and manipulate photons, Kumar’s team was able to strengthen the interaction between the microwave photons carrying the quantum information and the rubidium atoms used to transfer that information to optical photons. This allowed for more efficient and reliable transduction of quantum information, a critical step in developing practical quantum communication networks.
Although the chamber used by Kumar’s team may not seem enclosed, it is actually a carefully designed structure with a specific geometry that allows for the trapping of photons and atoms. The “Swiss cheese” appearance of the chamber is due to the presence of tunnels that intersect in a precise manner, creating traps at the intersection points. The design ensures that the trapped particles remain isolated from the surrounding environment, which is crucial for maintaining the delicate quantum states.
The access points to the chamber are also carefully placed to allow researchers to inject the atoms and photons needed for the experiment. This level of control over the experimental setup is essential for achieving the high levels of precision required for quantum experiments. The ability to inject and extract particles from the chamber is what allows the researchers to manipulate the quantum states of the atoms and photons trapped inside.
Kumar’s technology for transferring quantum information between different modes has enormous potential in the field of quantum computing. While it can be a vital building block for quantum networking, it can also improve other quantum technologies. The entanglement of atoms and photons is essential for a wide range of quantum applications, from quantum cryptography to quantum sensing.
The entanglement created by Kumar’s technology is much stronger than traditional methods, which makes it ideal for applications such as quantum sensing, where the precision of measurements is critical. By harnessing the power of strongly entangled atoms and photons, researchers can improve the accuracy of atomic clocks, develop more precise sensors for detecting gravitational waves, and even explore new avenues in quantum chemistry. Furthermore, the ability to convert quantum information between microwave and optical photons opens up new possibilities in quantum computing, where different hardware platforms can communicate seamlessly.
“One of the things that we’re really excited about is the ability of this platform to generate really efficient entanglement,” he said. “Entanglement is central to almost everything quantum that we care about, from computing to simulations to metrology and atomic clocks. I’m excited to see what else we can do.
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