High-fidelity two-qubit entangling gates play an important role in many quantum information processing tasks and are a necessary building block for constructing a universal quantum computer. Such high-fidelity gates have been demonstrated on trapped-ion qubits, however, control errors and noise in gate parameters may still lead to reduced fidelity. Here we propose and demonstrate a general family of two-qubit entangling gates which are robust to different sources of noise and control errors. These gates generalize the celebrated Mølmer-Sørensen gate by using multi-tone drives. We experimentally implemented several of the proposed gates on 88 Sr + ions trapped in a linear Paul trap, and verified their resilience. arXiv:1805.06806v1 [quant-ph]

Atomic isotope shifts (ISs) are the isotope-dependent energy differences in the atomic electron energy levels. These shifts serve an important role in atomic and nuclear physics, and particularly in the latter as signatures of nuclear structure. Recently ISs have been suggested as unique probes of beyond Standard Model (SM) physics, under the condition that they be determined significantly more precisely than current state of the art. In this work we present a simple and robust method for measuring ISs with ions in a Paul trap, by taking advantage of Hilbert subspaces that are insensitive to commonmode noise yet sensitive to the IS. Using this method we evaluate the IS of the 5S 1/2 ↔ 4D 5/2 transition in 86 Sr + and 88 Sr + with a 1.6 × 10 −11 relative uncertainty to be 570, 264,063.435(9) Hz. Furthermore, we detect a relative difference of 3.46(23) × 10 −8 between the orbital g-factors of the electrons in the 4D 5/2 level of the two isotopes. Our method is relatively easy to implement

The prevalent approach to executing quantum algorithms on quantum computers is to break-down the algorithms to a concatenation of universal gates, typically single and two-qubit gates. However such a decomposition results in long gate sequences which are exponential in the qubit register size. Furthermore, gate fidelities tend to decrease when acting in larger qubit registers. Thus high-fidelity implementations in large qubit registers is still a prominent challenge. Here we propose and investigate multi-qubit entangling gates for trapped-ions. Our gates couple many qubits at once, allowing to decrease the total number of gates used while retaining a high gate fidelity. Our method employs all of the normal-modes of motion of the ion chain, which allows to operate outside of the adiabatic regime and at rates comparable to the secular ion-trapping frequency. Furthermore we extend our method for generating Hamiltonians which are suitable for quantum analog simulations, such as a nearest-neighbour spin Hamiltonian or the Su-Schrieffer-Heeger Hamiltonian.

Engineering entanglement between quantum systems often involves coupling through a bosonic mediator, which should be disentangled from the systems at the operation's end. The quality of such an operation is generally limited by environmental and control noise. One of the prime techniques for suppressing noise is by dynamical decoupling, where one actively applies pulses at a rate that is faster than the typical time scale of the noise. However, for boson-mediated gates, current dynamical decoupling schemes require executing the pulses only when the boson and the quantum systems are disentangled. This restriction implies an increase of the gate time by a factor of √ N , with N being the number of pulses applied. Here we propose and realize a method that enables dynamical decoupling in a boson mediated system where the pulses can be applied while spin-boson entanglement persists, resulting in an increase in time that is at most a factor of π 2 , independently of the number of pulses applied. We experimentally demonstrate the robustness of our fast dynamically decoupled entangling gate to σz noise with ions in a Paul trap.High quality on-demand generation of entanglement is a necessary condition for quantum information processing and quantum metrology. While for some physical platforms entanglement is generated by an inherent direct interaction between subsystems, various platforms of interest make use of a mediating boson with spindependent coupling. For instance, the interaction between trapped ions is carried via a vibrational phonon [1][2][3][4][5][6][7][8][9][11][12][13]; superconducting qubits are entangled via a microwave photon [16][17][18]; the interaction between distant NVs can be carried via a nanomechanical oscillator's phonon [19,20] and a cavity photon carries the interaction between atoms in cavity QED architectures [21,23,24]. The common Hamiltonian representing these quantum systems is of the formwith σ α,i representing the Pauli matrix in the α direction of the i th spin. In the trapped ion case this Hamiltonian allows one to execute the Mølmer-Sørensen (MS) gate [1]. After times 2πn/ε for an integer n, the boson is disentangled from the spins, leaving the spins entangled via a geometric phase which is proportional to the area of the closed circle traced by the boson trajectory in phase space [2, 3,25].Despite considerable progress in achieving high-fidelity entanglement in recent years, entanglement fidelity remains a primary obstacle for performance of large scale quantum information processing, and more particularly fault-tolerant quantum computation. Attempts to improve the fidelity of entangling gates must overcome the limitations imposed by environmental noise as well as imperfections in the control apparatus. Dynamical decoupling is a common method for fighting the effects of noise. When utilizing dynamical decoupling pulses [26,27] during the entangling gate operation, one is required to consider the affect on the spin dependent coupling to the mediating boson. In many experiments, a sing...

We present a method that uses radio-frequency pulses to cancel the quadrupole shift in optical clock transitions. Quadrupole shifts are an inherent inhomogeneous broadening mechanism in trapped ion crystals, limiting current optical ion clocks to work with a single probe ion. Cancelling this shift at each interrogation cycle of the ion frequency allows the use of N > 1 ions in clocks, thus reducing the uncertainty in the clock frequency by √ N according to the standard quantum limit. Our sequence relies on the tensorial nature of the quadrupole shift, and thus also cancels other tensorial shifts, such as the tensor ac stark shift. We experimentally demonstrate our sequence on three and seven 88 Sr + ions trapped in a linear Paul trap, using correlation spectroscopy. We show a reduction of the quadrupole shift difference between ions to ≈ 20 mHz's level where other shifts, such as the relativistic 2 nd order Doppler shift, are expected to limit our spectral resolution. In addition, we show that using radio-frequency dynamic decoupling we can also cancel the effect of 1 st order Zeeman shifts.