Quantum for fundamental scientific discovery
There has been tremendous progress in the past century in understanding the fundamental laws governing the observable universe, yet many open questions remain. Among these questions, are there any fundamental particles or interactions that have not yet been discovered? What is the nature of dark matter and dark energy that make up 95% of the universe?
To answer these questions, we need better detector technologies that are more precise and more sensitive. Superconducting quantum sensors, quantum devices that are sensitive enough to probe discrete excitations of photons and phonons with high precision, are poised to enable the next generation of fundamental scientific discoveries.
Fermilab has a rich history of innovation in superconducting technologies, in both magnets and radio frequency cavities. Superconducting magnets enabled particle colliders with high energies to enable the discovery of fundamental particles, e.g., the Tevatron collider’s discovery of the top quark. Superconducting SRF cavities enabled linear accelerators such as the Linac Coherent Light Source II at SLAC National Laboratory, for which Fermilab contributed half the cryomodules, and the Proton Improvement Plan II, an essential enhancement of the Fermilab Accelerator Complex that will power the world’s most intense high-energy neutrino beam.
Fermilab continues this tradition of superconductor innovation by developing superconducting qubits and cavities with ultra-high coherence times at cryogenic temperatures as low as few millikelvin. Traditionally used to transfer energy to particle beams in accelerators, ultra-high quality factor (Q) cavities have emerged as a powerful tool for fundamental physics experiments. Their high quality factor enables long integration times, allowing weak signals, such as those from dark matter interactions, to build up resonantly. With minimal internal losses and the ability to filter out non-resonant background noise, SRF cavities significantly improve the signal-to-noise ratio by both amplifying the target signal and ensuring a cleaner detection environment, providing a powerful tool to search for new physics.
Our goals: Explore quantum technology advancements for fundamental physics.
- Are there new interactions and particles?
- What makes up the invisible Dark Matter in our Universe?
- What are the limits of quantum entanglement and the emergent properties of complex entangled states?
- Can we detect high-frequency gravitational waves?
Use the science drivers to push the development of sophisticated quantum devices and control techniques.
Demonstrate quantum advantage for fundamental science problems by:
- Pushing the exclusion boundary for axion or dark photon searches by more than one order of magnitude from the current state of the art;
- Push beyond the limits of quantum entanglement, building record-size cat states to explore the quantum-classical boundary.
Dark matter and new particles beyond the Standard Model
According to Newton’s law of gravity, the velocity that a planet needs to maintain to remain in a stable orbit depends on the total mass that resides in the center of its orbital motion. In 1930, Fritz Zwicky made the remarkable observation that galaxies in the Coma cluster orbit much faster than their combined mass can explain. Zwicky postulated the existence of a new form of invisible matter, which he named Dark Matter.
This strange form of matter only interacts via the force of gravity, and so does not produce any visible or other types of radiation to be detectable. Support for the existence of Dark Matter comes from astronomical observations that clusters of galaxies bend light more than expected. Dark Matter was abundantly produced during the Big Bang. As Dark Matter cooled, it began gravitational clumping, so galaxies started to form. Thus, Dark Matter is essential for a galaxy’s existence.
Dark Matter constitutes 23% of all the matter and energy in nature, as compared to 5% of ordinary, familiar matter. But its constituents are completely unknown and undetected, remaining one of the dominant mysteries of science today.
Dark photons?
There are various theoretical candidates for dark matter particles under exploration with special experiments. One candidate is the dark photon. Itsfascinating property (if it exists) is that it can go through walls! It is the invisible counterpart to photons. SQMS researchers demonstrated the deepest sensitivity to dark photons dark matter leveraging a ultra-high Q SRF cavity cooled down to few mK, and are now conducting a search using a new widely tunable cavity designed to search for dark photos over several Gigahertz.
In the Dark SRF experiment instead, SQMS researchers are using a pair of superconducting resonators, hunting for signals of non dark matter dark photons, trying to produce and detect this hypothesized particle in the laboratory, and have already established world-record sensitivity in a certain mass range and recently published an improved limit that further extends the Dark SRF sensitivity. With qubit sensors, these experiments are further increasing the sensitivity of detection, leading to discovery potential.
SQMS building devices for ultimate quantum sensing
Another candidate for Dark Matter is the Axion, named after a laundry detergent, to clean up a key problem in high-energy physics! It is a hypothetical particle with a mass 100 billion times less than that of the electron.
Axions were postulated to explain why Charge-Parity (CP) violation is not observed in strong interactions, although it should be – according to the Standard Model. It also plays a role in cosmology. Even though their mass could be in the range of micro-eV if axions exist, there could be so many of them in the Universe, that they contribute a large proportion of the overall mass of dark matter in the universe, and therefore 23% of all matter. By saturating a region with a very strong electromagnetic field, the axion may decay into two photons, which could be detected by quantum sensors that have the capability to detect single photons.
Discovery of axions would re-write the laws of particle physics and cosmology.
A strong magnetic field will coax dark matter out of hiding and convert axions into light particles inside a superconducting microwave resonator. The detector should be tuned to different frequencies corresponding to axions of different masses to scan over the possible mass of the dark matter. When equipped with ultrasensitive, low-noise quantum electronics the experiment can achieve even deeper sensitivity. The expected signal is at 10-23 watts or less.
Axion detection can be achieved by placing the cavity in a strong multi-Tesla external magnetic field (the standard haloscope method), or by performing a heterodyne search, and SQMS is actively pursuing both fronts. In axion haloscope experiments in high magnetic fields, quantum enhanced sensitivity can be achieved using a superconducting qubit chip placed outside of the cavity and of the magnetic field, with the goal of subverting the Standard Quantum Limit Noise and increasing the dark matter scan rate by orders of magnitude. SQMS and INFN have demonstrated the first implementation of an axion dark matter search with itinerant photon counting, leading to an increase in scan rate by a factor of 20.
On the axion heterodyne front, SQMS Superconducting Heterodyne Axion Dark Matter Experiment (SHADE), leverages two resonant modes within a single niobium SRF cavity to create the conditions necessary for converting ultralight axions into detectable photons, using lower magnetic fields, but taking full advantage of the high-quality factors.
SQMS is pushing several experiments in collaboration with INFN and other institutions, with cavities and qubits, some of which have already demonstrated world-leading devices and sensitivity and discovery potential for dark sector particles and axion-like particles, and even high frequency gravitational waves detection using SRF cavities.
