Trapped ions in the strong-excitation regime: Ion interferometry and nonclassical states

Three-Dimensional Matter-Wave Interferometry of a Trapped Single Ion

We report on a demonstration of Ramsey interferometry by three-dimensional motion with a trapped ^{171}Yb^{+} ion. We applied a momentum kick to the ion in a direction diagonal to the trap axes to initiate three-dimensional motion using a mode-locked pulse laser. The interference signal was analyzed theoretically to demonstrate three-dimensional matter-wave interference. This work paves the way to realizing matter-wave interferometry using trapped ions.

Effect of an echo sequence to a trapped single-atom interferometer with photon momentum kicks

We investigate a single-atom interferometer (SAI) in an optical dipole trap (ODT) with photon momentum kicks. An echo sequence is used for the SAI. We find experimentally that interference visibilities of a counter-propagating Raman type SAI decay much faster than the co-propagating case. To understand the underlying mechanism, a wave-packet propagating simulation is developed for the ODT-guided SAI. We show that in state dependent dipole potentials, the coupling between external dynamics and internal states makes the atom evolve in different paths during the interfering process. The acquired momentum from counter-propagating Raman pulses forces the external motional wave packets of two paths be completely separated and the interferometer visibility decays quickly compared to that of the co-propagating Raman pulses process. Meanwhile, the echo interference visibility experiences revival or instantaneous collapse which depends on the π pulse adding time at approximate integer multiples or half integer multiples of the trap period.

Engineering SU(1, 1) ⊗ SU(1, 1) vibrational states

We propose an ideal scheme for preparing vibrational SU(1, 1) ⊗ SU(1, 1) states in a two-dimensional ion trap using red and blue second sideband resolved driving of two orthogonal vibrational modes. Symmetric and asymmetric driving provide two regimes to realize quantum state engineering of the vibrational modes. In one regime, we show that time evolution synthesizes so-called SU(1, 1) Perelomov coherent states, that is separable squeezed states and their superposition too. The other regime allows engineering of lossless 50/50 SU(2) beam splitter states that are entangled states. These ideal dynamics are reversible, thus, the non-classical and entangled states produced by our schemes might be used as resources for interferometry.

Sensing Atomic Motion from the Zero Point to Room Temperature with Ultrafast Atom Interferometry

We sense the motion of a trapped atomic ion using a sequence of state-dependent ultrafast momentum kicks. We use this atom interferometer to characterize a nearly pure quantum state with n=1 phonon and accurately measure thermal states ranging from near the zero-point energy to n[over ¯]~10^{4}, with the possibility of extending at least 100 times higher in energy. The complete energy range of this method spans from the ground state to far outside of the Lamb-Dicke regime, where atomic motion is greater than the optical wavelength. Apart from thermometry, these interferometric techniques are useful for characterizing ultrafast entangling gates between multiple trapped ions.

Ultrafast spin-motion entanglement and interferometry with a single atom

We report entanglement of a single atom's hyperfine spin state with its motional state in a time scale of less than 3 ns. We engineer a short train of intense laser pulses to impart a spin-dependent momentum transfer of ± 2 ħk. Using pairs of momentum kicks, we create an atomic interferometer and demonstrate collapse and revival of spin coherence as the motional wave packet is split and recombined. The revival after a pair of kicks occurs only when the second kick is delayed by an integer multiple of the harmonic trap period, a signature of entanglement and disentanglement of the spin with the motion. Such quantum control opens a new regime of ultrafast entanglement in atomic qubits.

Deep strong coupling regime of the Jaynes-Cummings model

We study the quantum dynamics of a two-level system interacting with a quantized harmonic oscillator in the deep strong coupling regime (DSC) of the Jaynes-Cummings model, that is, when the coupling strength g is comparable or larger than the oscillator frequency ω (g/ω≳1). In this case, the rotating-wave approximation cannot be applied or treated perturbatively in general. We propose an intuitive and predictive physical frame to describe the DSC regime where photon number wave packets bounce back and forth along parity chains of the Hilbert space, while producing collapse and revivals of the initial population. We exemplify our physical frame with numerical and analytical considerations in the qubit population, photon statistics, and Wigner phase space.

Ultrafast gates for single atomic qubits

We demonstrate single-qubit operations on a trapped atom hyperfine qubit using a single ultrafast pulse from a mode-locked laser. We shape the pulse from the laser and perform a π rotation of the qubit in less than 50 ps with a population transfer exceeding 99% and negligible effects from spontaneous emission or ac Stark shifts. The gate time is significantly shorter than the period of atomic motion in the trap (Ω(Rabi)/ν(trap)>10(4)), demonstrating that this interaction takes place deep within the strong excitation regime.

Entanglement of atomic qubits using an optical frequency comb

We demonstrate the use of an optical frequency comb to coherently control and entangle atomic qubits. A train of off-resonant ultrafast laser pulses is used to efficiently and coherently transfer population between electronic and vibrational states of trapped atomic ions and implement an entangling quantum logic gate with high fidelity. This technique can be extended to the high field regime where operations can be performed faster than the trap frequency. This general approach can be applied to more complex quantum systems, such as large collections of interacting atoms or molecules.

Ultrafast coherent excitation of a trapped ion qubit for fast gates and photon frequency qubits

We demonstrate ultrafast coherent excitation of an atomic qubit stored in the hyperfine levels of a single trapped cadmium ion. Such ultrafast excitation is crucial for entangling networks of remotely located trapped ions through the interference of photon frequency qubits, and is also a key component for realizing ultrafast quantum gates between Coulomb-coupled ions.