Thompson Group - Entanglement & Matterwaves
Rb: Entanglement & Matterwaves
We laser cool rubidium atoms to microKelvin temperatures and trap them using optical lattices inside of a high finesse cavity. The high finesse cavity allows the light to interact with the atoms many times to create strong collective coupling between an ensemble of nearly a million atoms and optical modes of the cavity. Learn more below about our research including:
- Highly-entangled states using quantum non-demolition measurements and cavity-mediated interactions
- The first entanglement-enhanced matterwave interferometer
- XYZ Hamiltonian engineering
- Gluing matterwave packets together with light
- Superradiant lasers with < 1 photon inside the cavity
- Novel magnetometers
- Novel laser cooling
Entangled Spin Squeezed States via Quantum Nondemolition Measurements
Quantum metrology with atoms is extremely powerful because the laws of quantum mechanics provides a quantumÌýcertaintyÌýthat atoms of a given type are identical. ÌýThis allows us to build sensors of time, magnetic and electric fields, accelerations, and rotations, and apply these sensors to search forÌýnew physics. ÌýHowever, the price we pay for this quantum certainty, is that the measurement precision is limited by quantumÌý³Ü²Ô³¦±ð°ù³Ù²¹¾±²Ô³Ù²âÌýprinciples that we are more familiar with and in this context referred to as the Standard Quantum Limit.Ìý By entangling the atoms, one can create states in which the atoms conspire together to partially cancel each atom's quantum noise. ÌýOne example of this is a spin squeezed state in which the orientation of a collection of spins in a real or pseudo space has angular uncertainty in its orientation that can be squeezed in one direction at the expense of noise in another angular direction that does not impact your experiment.
We utilize the quantum measurement process to create some of the largest amounts of entanglement every directly detected, surpassing the Standard Quantum Limit on phase estimation by a factor of 60 or about 18 dB. ÌýThis collective or quantum nondemolition (QND)Ìýmeasurement approach is very powerful. ÌýWith only a 50 microsecond measurement pulse of light, we can create a state with measurementÌýsensitivityÌýequivalent to that ofÌý10,000 perfect copies of 60 atom perfect cat states. ÌýSuch states are well out of range of any current microscopic approaches to entanglement generation, and hold great promise for application in state of the art atom interferometers andÌýatomic clocks.
Superradiance: Lasing with <1 photon
We have demonstrated a laser that operates with as few as 0.2 photons in the lasing cavity. ÌýIn a normal laser, the photons act as the flywheel or phase memory for the laser, but in this special regime called superradiance the atoms act as the laser's flywheel or phase memory. ÌýIn fact, we showed that oneÌýcan completely empty the cavity of photons, and the phased array antenna formed by the atomic ensemble still kept track of the phase. ÌýIn fact, these results launched our lab's other efforts using strontium to realize ultranarrow frequency lasers. ÌýWe have demonstrated hybrid active/passive lasing technique to realize a Ramsey-like sequence without population measurements, studied relaxation oscillations in the superradiant regime, utilized superradiance and dynamical techniques to realize an active magnetometer, and explored the fundamental physics of how disspation produces synchronization in the superradiant regime.ÌýÌýIn the future, we plan to use the interference between two different superradiant lasing processes to realize a theoretical proposal with the Holland group to create a continuous quantum nondemolition measurement that will continuously track a quantum phase below the standard quantum limit.
SWAP Laser Cooling with Synthetic Optical Transitions
We have demonstrated a novel laser cooling approachÌýin which swept frequency lasers generate adiabatic passage to states of lower total momentum, leading to cooling of the atomic ensemble. ÌýThe technique relies on the atom being in a long lived state between the adiabatic photon absorption process and the adiabatic photon stimulation process that removes 2 photon recoil momenta per laser sweep. ÌýWe demonstrated that synthetic excited states can be employed instead of true long-lived optical excited states. ÌýThis opens the range of atomic and molecular systems to which this laser cooling technique could be applied.