An international team of physicists reports that they have successfully produced a Bose-Einstein condensate in space for the first time. In the study published this past week in Nature, the group describes how they created a small device capable of producing a Bose-Einstein condensate, attached it to a rocket, and the experiments that were conducted during freefall.
By doing so, the team was able to observe the dynamics and phase transitions of the quantum gas for a period of time orders of magnitude larger than previous experimental techniques.
The study represents a leap forward in technology and experimental techniques involving Bose-Einstein condensates. Bose-Einstein condensates are notoriously difficult to produce and sustain, and even more difficult to perform experiments on. The microgravity environment of freefall provides an isolated area in which a Bose-Einstein condensate can be thoroughly observed.
Additionally, the team created a device capable of producing robust BECs that is small enough for transport and easy installation. Applications of the quantum gas include ultra-sensitive interferometers, sensors, room temperature superconductors, and quantum computers. According to the study, the success of the experiment “opens a new era for quantum gas experiments.” The paper can be read in full on the preprint publication arXiv.
Bose-Einstein Condensates And Freefall Environments
A Bose-Einstein condensate (BEC)is a state of matter created by cooling a gas of bosonic particles to temperatures extremely close to absolute zero. When cooled to such temperatures, the particles begin to occupy the lowest possible energy state and quantum phenomena like particle-wave duality and wave function interference become apparent on macroscopic (molecular) scales. BECs exhibit a number of strange properties such as superfluidity, superconductivity, and an exaggerated wave-like nature.
Because they exist at such low-energy states, BECs react to even the smallest change in kinetic energy. This property makes them theoretically useful for sensors for detecting gravity waves, as they are capable of registering changes in kinetic energy corresponding to temperatures in the pico- or femto-Kelvin region. (1 quadrillionth of a degree Kelvin). However, in terrestrial environments, the presence of gravity often interferes with the structure of the gas, preventing clear observation. As such, most observations of BECs have involved dropping them off of tall towers so that observations can be made during the freefall when no net gravity force is acting on the apparatus. Simply dropping it off of a tower only gives a window of a few seconds to make observations though.
So, the team had the brilliant idea of literally shooting a BEC into space to take advantage of the elongated freefall as the rocket falls back to earth. The microgravity environment of space would allow observation times orders of magnitude longer than previous experiments. Notoriously difficult to produce and contain, BECs are normally created in large specialized chambers so the team had to figure out a way to miniaturize that design into something that could fit onto a 300kg rocket. The final device consisted of a capsule containing a chip holding a group of rubidium-87 atoms, precise lasers, electronics, and a power source. The team placed their device on board the MAIUS I rocket, launched out of Kiruna, Sweden in January 2017 for a space flight that lasted 6 minutes. During that time, the team was able to run hundreds of experiments during the initial takeoff, acceleration, and ensuing freefall. Specifically, the team investigated laser cooling and trapping of particles during the acceleration of takeoff, and the evolution and manipulation of BECs using matter-wave interferometry techniques. Although the experiments were run over a year ago, we are just now seeing the completed analysis of data gathered during the flight.
At the height of the trip, the chip cooled the rubidium-87 atoms to a temperature of -273.15°C—almost one full degree colder than the coldest natural place in the universe, the Boomerang Nebula. So for 6 minutes, the experimental device had the honor of being the coldest object in the known universe.
One of the proposed applications of BECs is to help in the search for gravity waves. To detect these extremely tiny ripples in space-time, astrophysicists currently will split laser beams and recombine them. Discrepancies in the wave pattern show signs of interference and can indicate the presence of a gravity wave. This was the technique used by LIGO researchers to make the first direct observation of a gravity wave in 2016. The experiments run on the rocket showed the BECs could provide an alternative method for detecting gravity waves.
The team used lasers to split the cloud of particles in half and then recombine them. Since the particles in each half share the exact same state, when they recombine, any changes in the wave pattern could indicate the external influence of a gravity wave. Because BECs express changes in behavior corresponding to kinetic energy input on the femto-Kelvin scale, they would be an ideal substance to detect the presence of extremely low energy gravity waves. On Earth, there is not enough time in freefall to detect the ineffable changes but the microgravity environment of space allows for unobstructed temporally robust measurements.
NASA has already realized the potential for a space-based platform for conducting BEC research and is currently in the process of setting up the Cold Atom Laboratory (CAL) on the ISS, though it is not fully functional yet. In the meantime, the team has demonstrated the fruitfulness of running experiments on BECs in the microgravity environment of space. More MAUIS missions are planned for the future.
In addition to providing a wealth of detailed observations of the dynamics and phase transitions of BECs, the team created a device capable of making robust and stable BECs small enough to be sent into space for relatively little cost. BECs are being investigated for their applications in quantum computers and communications systems so miniaturizing photon-based quantum information concepts could pave the way towards quantum communications satellites, making the quantum internet a reality.