The Konrad Lehnert and Cindy Regal groups collaborate on exploring the quantum behavior of tiny mechanical drums, or resonators that are large enough to be visible to the naked eye. They use electricity to achieve exquisite control and measurement of the drums. These experiments allow them to explore the interface between the everyday physical world and the mysterious quantum world.
The Squeeze Machine
The Regal group has built a miniature light-powered machine that can strip away noise from a laser beam. To accomplish this, the group found a creative way to work around the quantum limit imposed by the Heisenberg Uncertainty Principle. The uncertainty principle makes it impossible to simultaneously reduce the noise on both the amplitude and phase of light inside interferometers and other high-tech instruments that detect miniscule position changes.
The group got around this limit by squeezing the quantum state of its laser light. In the process, the researchers reduced the amount of quantum noise in the amplitude, make it possible to use the squeezed laser light to make more precise measurements. However, the noise reduction in the light amplitude came at the cost of increasing the amount of quantum noise in the phase of the laser light. So no laws of quantum mechanics were violated.
The group squeezed the laser light by having it interact with a tiny vibrating drum inside an optical cavity. The use of the drum is a key feature of the squeeze machine because it provides tailored squeezed light for interferomenters for precision measurement. The laser light exerts a force on the drum, which links together the phase and amplitude of the light inside the cavity. By taking advantage of this linkage, the researchers were able to arrange for the amplitude of the light to have 32% less quantum noise than it otherwise would have had. The research team was also able to show squeezing over different ranges by looking a various combinations of the amplitude and phase noise.
This experiment may lead to improvements in precision measurement in gravitational-wave detectors and in state-of-the-art microscopy.
The Konrad Lehnert group has figured out how to transport and store quantum information. Researchers have encoded a quantum state onto an electric circuit and transported the information from the circuit into a tiny mechanical drum for storage. The group retrieves the stored information by reconverting it into an electrical signal. This scheme opens the door to using tiny drums for memory storage in quantum computers and as intermediaries in systems that convert quantum information from one physical system, such as a microwave field, to another physical system such as a laser light field.
In this new transportation scheme, voltages oscillations describing a quantum state in an electrical signal are transformed into mechanical energy (vibrations) in the drum. The drum can store quantum information for much longer than can an electrical signal. And, the drum vibrations can be reconverted into an electrical signal at any time—as long as the drum is still vibrating.
This new information transporter is already playing a role in transferring quantum information from a microwave light field to a laser light field. These two forms of electromagnetic radiation cannot communicate with each other on the quantum level. The Lehnert/Regal collaboration succeeded in building a transporter connecting a vibrating drum with a laser light field, opening the door to building a supertransporter to send quantum information back and forth between a microwave field (the realm of electronic devices) to a visible light field. Such an information supertransporter could open the door to quantum systems engineering on an unprecedented scale.
Nano Mechanical Drums
One project in the Cindy Regal lab seeks ways to prolong vibrations in mechanical objects such as drums or strings. The ability to prolong vibrations makes it possible to laser cool objects to temperatures where it is possible to observe quantum mechanical motion.
The researchers are investigating how changes in shape affect the vibration patterns of 50-nm-thick membranes made of silicon nitride (Si3N4). They are also exploring how holes in the membranes affect their interactions with the silicon holder.
The Regal group recently completed a set of experiments that helped it better understand the properties of the drums that influence the lifetime of their vibrations. For this work, the group used a series of two-layer drums of aluminum metal and Si3N4 that were 1-mm squares with a thickness of 100 nm. The researchers discovered the metal layer made drum vibrations disappear more rapidly.
The cause of this damping was the behavior of the drum at its very edge, which was a thousandth of a millimeter wide. When the researchers applied aluminum metal to most of the center of a Si3N4 drum, the vibrations lasted just as long as they did in a simple Si3N4 drum. They will use this knowledge to design advanced hybrid drums in the future.
Ongoing experiments include a series of investigations of very high-tension 50-nm Si3N4 membranes. Such membranes are considered near ideal for studying the interactions of light with nanomechanical systems, including electric circuits. They will likely play a role in efforts to create a quantum interface between light and mechanical motion.