Research Highlights

The process of developing a quantum computer has seen significant progress in the past 20 years. Quantum computers are designed to solve complex problems using the intricacies of quantum mechanics. These computers can also communicate with each other by using entangled photons (photons that have connected quantum states). As a result of this entanglement, quantum communication can provide a more secure form of communication, and has been seen as a promising method for the future of a more private and faster internet.

Qubits are a basic building block for quantum computers, but they’re also notoriously fragile—tricky to observe without erasing their information in the process. Now, new research from CU Boulder and the National Institute of Standards and Technology (NIST) may be a leap forward for handling qubits with a light touch.  

In the study, a team of physicists demonstrated that it could read out the signals from a type of qubit called a superconducting qubit using laser light—and without destroying the qubit at the same time.

Artist's depiction of an electro-optic transducer, an ultra-thin wafer that can read out the information from a superconducting qubit.

Artist's depiction of an electro-optic transducer, an ultra-thin device that can capture and transform the signals coming from a superconducting qubit. (Credit: Steven Burrows/JILA)

The group’s results could be a major step toward building a quantum internet, the researchers say. Such a network would link up dozens or even hundreds of quantum chips, allowing engineers to solve problems that are beyond the reach of even the fastest supercomputers around today. They could also, theoretically, use a similar set of tools to send unbreakable codes over long distances. 

The study, published June 15 in the journal Nature, was led by JILA, a joint research institute between CU Boulder and NIST.

In a new paper published in Physical Review Letters, JILA and NIST Fellows Eric Cornell, Jun Ye, and Konrad Lehnert developed a method for measuring a potential dark matter candidate, known as an axion-like particle. Axion-like particles are a potential class of dark matter particle which could explain some aspects of galactic structure. This work is also a result of collaboration with Victor Flambaum who is a leading theorist studying possible violations of fundamental symmetries. 

For nearly a century, scientists have worked to unravel the mystery of dark matter—an elusive substance that spreads through the universe and likely makes up much of its mass, but has so far proven impossible to detect in experiments. Now, a team of researchers have used an innovative technique called “quantum squeezing” to dramatically speed up the search for one candidate for dark matter in the lab. 

Quantum drums can get around distracting noise with a new measurement technique—one that perfectly demonstrates the Heisenberg uncertainty principle.

How do you hear--and study--the quietest sound in the universe? With a special microphone and speaker. 

Quantum computers are set to revolutionize society. With their expansive power and speed, quantum computers could reduce today’s impossibly complex problems, like artificial intelligence and weather forecasts, to mere algorithms. But as revolutionary as the quantum computer will be, its promises will be stifled without the right connections. Peter Burns, a JILA graduate student in the Lehnert/Regal lab, likens this stifle to a world without Wi-Fi.  

Quantum computers require systems that can encode, manipulate, and transmit quantum bits, or qubits. A creative way to accomplish all this was recently demonstrated by Adam Reed and his colleagues in the Lehnert group. The researchers converted propagating qubits (encoded as superpositions1 of zero and one microwave photons) into the motion of a tiny aluminum drum. The successful conversion is considered a key step in using a mechanical drum to (1) transfer quantum information between microwave and optical frequencies or (2) store quantum information inside a quantum computer.

The Regal group recently met the challenge of measurements in an extreme situation with a device called an interferometer. The researchers succeeded by using creative alterations to the device itself and quantum correlations. Quantum correlations are unique, and often counterintuitive, quantum mechanical interactions that occur among quantum objects such as photons and atoms. The group exploited these interactions in the way they set up their interferometer, and improved its ability to measure tiny motions using photons (particles of light).

The first results are in from a new search for the axion, a hypothetical particle that may constitute dark matter. Researchers in the Haloscope At Yale Sensitive to Axion Cold Dark Matter (HAYSTAC) recently looked for evidence of the axion, but so far they have found none in the small 100 MHz frequency range between 5.7 and 5.8 GHz.

Bob Peterson and his colleagues in the Lehnert-Regal lab recently set out to try something that had never been done before: use laser cooling to systematically reduce the temperature of a tiny drum made of silicon nitride as low as allowed by the laws of quantum mechanics. Although laser cooling has become commonplace for atoms, researchers have only recently used lasers to cool tiny silicon nitride drums, stretched over a silicon frame, to their quantum ground state. Peterson and his team decided to see just how cold their drum could get via laser cooling.

In the future, quantum microwave networks may handle quantum information transfer via optical fibers or microwave cables. The evolution of a quantum microwave network will rely on innovative microwave circuits currently being developed and characterized by the Lehnert group. Applications for this innovative technology could one day include quantum computing, converters that transform microwave signals to optical light while preserving any encoded quantum information, and advanced quantum electronics devices.

The Regal-Lehnert collaboration has just taken a significant step towards the goal of one day building a quantum information network. Large-scale fiber-optic networks capable of preserving fragile quantum states (which encode information) will be necessary to realize the benefits of superfast quantum computing.

Tauno Palomaki and his colleagues in the Lehnert group have just gone where no one has gone before: They’ve entangled the quantum motion of a vibrating drum with the quantum state of a moving electrical pulse. What’s more, they figured out how to storehalf of this novel entangled state in the drum (which is tiny compared to a musical drum, but huge compared to the atoms or molecules normally entangled in a lab). The drum can then generate another electrical pulse that is entangled with the first one!  This amazing feat was reported in Science.

In the future, quantum microwave networks may handle quantum information transfer via optical fibers or microwave cables. The evolution of a quantum microwave network will rely on innovative microwave circuits currently being developed and characterized by the Lehnert group. Applications for this innovative technology could one day include quantum computing, converters that transform microwave signals to optical light while preserving any encoded quantum information, and advanced quantum electronics devices.

The Lehnert group has come up with a clever way to transport and store quantum information. Research associate Tauno Palomaki, graduate student Jennifer Harlow, NIST colleagues Jon Teufel and Ray Simmonds, and Fellow Konrad Lehnert have encoded a quantum state onto an electric circuit and figured out how to transport the information from the circuit into a tiny mechanical drum, where is stored. Palomaki and his colleagues can retrieve the information by reconverting it into an electrical signal.

The Lehnert group and collaborators from the National Institute of Standards and Technology (NIST) recently made what was essentially a CT scan of the quantum state of a microwave field. The researchers made 100 measurements at different angles of this quantum state as it was wiggling around. Because they only viewed the quantum state from one angle at a time, they were able to circumvent quantum uncertainties to make virtually noiseless measurements of amplitude changes in their tiny microwave signals. Multiple precision measurements of the same quantum state yielded a full quantum picture of the microwave field.

Fellows Deborah Jin, Jun Ye, and John Bohn are exploring new scientific territory in cold-molecule chemistry. Experimentalists Jin and Ye and their colleagues can now manipulate, observe, and control ultralow-temperature potassium-rubidium (KRb) molecules in their lowest quantum-mechanical state. Theorist Bohn analyzes what the experimentalists see and predicts molecule behaviors under different conditions.

Not content with stepping on their bathroom scales each morning to watch the arrow spin round to find their weights, former research associate John Teufel and Fellow Konrad Lehnert decided to build a nifty system that could measure more diminutive forces of half an attoNewton (0.5 x 10^-18 N). Their new system consists of a tiny oscillating mechanical wire embedded in a microwave cavity with an integrated microwave interferometer, two amplifiers (one of them virtually noiseless), and a signal detector.

Fellow Konrad Lehnert needed a virtually noiseless amplifier to help with his experiments on nanoscale structures, so he invented one. Working with graduate student Manuel Castellanos-Beltran and NIST scientists Kent Irwin, Gene Hilton, and Leila Vale, he conceived a tunable device that operates in frequencies ranging from 4 to 8 GHz. This device has the lowest system noise ever measured for an amplifier. In fact, it produces 80 times less noise than the best commercial amplifier. More importantly, it adds no noise to a measurement system — a critical feature for a system probing the quantum limits of measurement.