Sub-GeV dark matter detection with quantum sensors

5 problems

• Can daily modulation in anisotropic crystals identify light dark matter?

  Open

  In a crystal that responds differently along different directions, the signal from dark matter should rise and fall once a day as Earth rotates, while most backgrounds should not. This could distinguish a real signal from the unexplained excess of small events.

• Can detectors reach the sub-MeV freeze-in dark matter benchmark?

  Partially resolved

  In one favored scenario, light dark matter was slowly produced in the early universe through a very light force carrier, which fixes how often it should scatter off electrons. Silicon detectors now exclude this scenario over much of the MeV to GeV range, but lighter dark matter carries too little energy to free an electron in silicon.

• Can single-magnon counting probe spin-coupled sub-MeV dark matter?

  Open

  In a magnet, spins can ripple together as a wave whose smallest unit is a magnon; dark matter that couples to electron spins could create one. Single magnons have been detected with a quantum bit, but no detector yet has the size and low noise needed for a dark matter search.

• Does the Migdal effect occur at the predicted rate in detector media?

  Partially resolved

  When a nucleus is hit suddenly, its electrons may be shaken loose, giving a detectable signal even from very light dark matter; this is the Migdal effect. It has now been seen directly, but searches in liquid xenon have not found it at the predicted rate.

• Can calorimeters detect single optical phonons with low background?

  Open

  Dark matter between about a hundred and a hundred thousand times lighter than a proton would make a crystal vibrate with only one quantum of vibration energy, a few hundredths of an electron volt. Detectors are not yet sensitive enough to count these single quanta.