Optical Manipulation of Qubits
Trapped ion qubits can be precisely controlled by laser beams
Once atomic ions are trapped and laser-cooled inside our vacuum chamber, we encode the qubit states |0⟩ and |1⟩ in two suitably chosen internal energy levels. In our experiments, we use the ground-state hyperfine levels because these qubits exhibit long coherence times. By shining precisely controlled laser light onto an individual ion, we can manipulate its qubit state. A central theme of our research is controlling trapped-ion qubits with laser beams. We pursue two complementary approaches: coherent and incoherent control.
Coherent control of qubits
To control qubit states coherently, meaning without deliberately (or inadvertently) measuring the qubit, we use laser beams that are far detuned from any atomic resonance. This type of control is essential for implementing quantum logic gates and for engineering Hamiltonians in quantum simulation experiments.
Although each laser beam is far from resonance, we exploit quantum-mechanical processes such as two-photon Raman transitions to drive transitions between the qubit levels.
Incoherent control of qubits
Laser light is also used to reset and measure qubits. This regime is, in spirit, the opposite of coherent control. Here we tune the laser beams to resonance so that the qubit absorbs light in a state-dependent manner, is excited, and then scatters photons as it returns to the ground state.
One novel research direction is in situ mid-circuit measurement: measuring a target qubit while preventing accidental measurement of neighboring qubits.
Check back soon for more details.