Ryan Bowler

Multi-element logic gates for trapped-ion qubits

Precision control over hybrid physical systems at the quantum level is important for the realization of many quantum-based technologies. In the field of quantum information processing (QIP) and quantum networking, various proposals discuss the possibility of hybrid architectures where specific tasks are delegated to the most suitable subsystem. For example, in quantum networks, it may be advantageous to transfer information from a subsystem that has good memory properties to another subsystem that is more efficient at transporting information between nodes in the network. For trapped ions, a hybrid system formed of different species introduces extra degrees of freedom that can be exploited to expand and refine the control of the system. Ions of different elements have previously been used in QIP experiments for sympathetic cooling, creation of entanglement through dissipation, and quantum non-demolition measurement of one species with another. Here we demonstrate an entangling quantum gate between ions of different elements which can serve as an important building block of QIP, quantum networking, precision spectroscopy, metrology, and quantum simulation. A geometric phase gate between a 9Be+ ion and a 25Mg+ ion is realized through an effective spin–spin interaction generated by state-dependent forces induced with laser beams. Combined with single-qubit gates and same-species entangling gates, this mixed-element entangling gate provides a complete set of gates over such a hybrid system for universal QIP. Using a sequence of such gates, we demonstrate a CNOT (controlled-NOT) gate and a SWAP gate. We further demonstrate the robustness of these gates against thermal excitation and show improved detection in quantum logic spectroscopy. We also observe a strong violation of a CHSH (Clauser–Horne–Shimony–Holt)-type Bell inequality on entangled states composed of different ion species.

Sympathetic electromagnetically-induced-transparency laser cooling of motional modes in an ion chain.

We use electromagnetically induced transparency (EIT) laser cooling to cool motional modes of a linear ion chain. As a demonstration, we apply EIT cooling on Mg ions to cool the axial modes of a Be-Mg ion pair and a Be-Mg-Mg-Be ion chain, thereby sympathetically cooling the Be ions. Compared to previous implementations of conventional Raman sideband cooling, we achieve approximately an order-of-magnitude reduction in the duration required to cool the modes to near the ground state and significant reduction in required laser intensity.

Measurement of the branching ratio in the6P3∕2decay ofBaIIwith a single trapped ion

We present a measurement of the branching ratios from the 6P3/2 state of BaII into all dipoleallowed decay channels (6S1/2, 5D3/2 and 5D5/2). Measurements were performed on single 138Ba+ ions in a linear Paul trap with a frequency-doubled mode-locked Ti:Sapphire laser resonant with the 6S1/2->6P3/2 transition at 455 nm by detection of electron shelving into the dark 5D5/2 state. By driving a pi Rabi rotation with a single femtosecond pulse, a absolute measurement of the branching ratio to 5D5/2 state was performed. Combined with a measurement of the relative decay rates into 5D3/2 and 5D5/2 states performed with long trains of highly attenuated 455 nm pulses, it allowed the extraction of the absolute ratios of the other two decays. Relative strengths normalized to unity are found to be 0.756+/-0.046, 0.0290+/-0.0015 and 0.215+/-0.0064 for 6S1/2, 5D3/2 and 5D5/2 respectively. This approximately constitutes a threefold improvement over the best previous measurements and is a sufficient level of precision to compare to calculated values for dipole matrix elements.

Rapid cooling to quantum degeneracy in dynamically shaped atom traps

We report on a general method for the rapid production of quantum degenerate gases. Using 174Yb, we achieve an experimental cycle time as low as (1.6-1.8) s for the production of Bose-Einstein condensates (BECs) of (0.5-1) x 10^5 atoms. While laser cooling to 30\muK proceeds in a standard way, evaporative cooling is highly optimized by performing it in an optical trap that is dynamically shaped by utilizing the time-averaged potential of a single laser beam moving rapidly in one dimension. We also produce large (>10^6) atom number BECs and successfully model the evaporation dynamics over more than three orders of magnitude in phase space density. Our method provides a simple and general approach to solving the problem of long production times of quantum degenerate gases.