PACS numbers:Quantum entanglement is the central resource behind applications in quantum information science, from quantum computers [1] and simulators of complex quantum systems [2] to metrology [3] and secure communication [1]. All of these applications require the quantum control of large networks of quantum bits (qubits) to realize gains and speedups over conventional devices. However, propagating quantum entanglement generally becomes difficult or impossible as the system grows in size, owing to the inevitable decoherence from the complexity of connections between the qubits and increased couplings to the environment. Here, we demonstrate the first step in a modular approach [4] to scaling entanglement by utilizing a hierarchy of quantum buses on a collection of three atomic ion qubits stored in two remote ion trap modules. Entanglement within a module is achieved with deterministic near-field interactions through phonons [5], and remote entanglement between modules is achieved through a probabilistic interaction through photons [6]. This minimal system allows us to address generic issues in synchronization and scalability of entanglement with multiple buses, while pointing the way toward a modular large-scale quantum computer architecture that promises less spectral crowding and less decoherence. We generate this modular entanglement faster than the observed qubit decoherence rate, thus the system can be scaled to much larger dimensions by adding more modules.Small modules of qubits have been entangled through native local interactions in many physical platforms, such as trapped atomic ions through their Coulomb interaction [5], Rydberg atoms through their electric dipoles [7,8], nitrogen-vacancy centers in diamond through their magnetic dipoles [9], and superconducting Josephson junctions through capacitive or inductive couplings [10,11]. However, each of these systems is confronted with practical limits to the number of qubits that can be reliably controlled, stemming from inhomogeneities, the complexity and density of the interactions between the qubits, or quantum decoherence. Scaling beyond these limits can be achieved by invoking a second type of interaction that can extend the entanglement to other similar qubit modules. Such an architecture should therefore exploit both the local interactions within the qubit modules, and also remote interactions between modules (an example architecture is shown in Fig 1). Optical interfaces provide ideal buses for this purpose [12,13], as optical photons can propagate over macroscopic distances with negligible loss. Several qubit systems have been entangled through remote optical buses, such as atomic ions [14], neutral atoms [15], and nitrogen-vacancy centers in diamond [16].In the experiment reported here, we juxtapose local and remote entanglement buses utilizing trapped atomic ion qubits, balancing the requirements of each interface within the same qubit system. The observed entanglement rate within and between modules is faster than the observed entangled qub...

The effects of two-photon exchange corrections, suggested to explain the difference between measurements of the proton elastic electromagnetic form factors using the polarization transfer and Rosenbluth techniques, have been studied in elastic and inelastic scattering data. Such corrections could introduce ε-dependent non-linearities in inelastic Rosenbluth separations, where ε is the virtual photon polarization parameter. It is concluded that such non-linear effects are consistent with zero for elastic, resonance, and deep-inelastic scattering for all Q 2 and W 2 values measured.

We measure ion heating following transport throughout a Y-junction surface-electrode ion trap. By carefully selecting the trap voltage update rate during adiabatic transport along a trap arm, we observe minimal heating relative to the anomalous heating background. Transport through the junction results in an induced heating between 37 and 150 quanta in the axial direction per traverse. To reliably measure heating in this range, we compare the experimental sideband envelope, including up to fourth-order sidebands, to a theoretical model. The sideband envelope method allows us to cover the intermediate heating range inaccessible to the first-order sideband and Doppler recooling methods. We conclude that quantum information processing in this ion trap will likely require sympathetic cooling in order to support high fidelity gates after junction transport. measurements for a stationary ion, ion motion in the linear region, and ion motion through the junction. In Sec. V, we conclude with a discussion of trap robustness and potential future directions.

A global nucleon-nucleus optical potential for elastic scattering has been produced which replicates experimental data to high accuracy and compares well with other recently formulated potentials. The calculation that has been developed describes proton and neutron scattering from target nuclei ranging from carbon to nickel and is applicable for projectile energies from 30 to 160 MeV. With these ranges it is suitable for calculations associated with experiments performed by exotic beam accelerators. The potential has both real and imaginary isovector asymmetry terms to better describe the dynamics of chains of isotopes and mirror nuclei. An analysis of the validity and strength of the asymmetry term is included with connections established to other optical potentials and charge-exchange reaction data.

No abstract

Selective laser addressing of a single atom or atomic ion qubit can be improved using narrowband composite pulse sequences. We describe a Lie-algebraic technique to generalize known narrowband sequences and introduce new sequences related by dilation and rotation of sequence generators. Our method improves known narrowband sequences by decreasing both the pulse time and the residual error. Finally, we experimentally demonstrate these composite sequences using 40 Ca + ions trapped in a surface-electrode ion trap.PACS numbers: 03.67. Lx, 32.80.Qk, 37.10.Ty In ion trap quantum computers [1,2] and neutral atom optical lattices [3,4], single-qubit addressing typically requires focused lasers where the beam waist is smaller than the inter-atom separation. Closely spaced atoms are generally desirable to improve two-qubit coupling rates, often demanding inter-atom spacings approaching the diffraction limit. In practice, single-qubit addressing requires precise focal alignment and ultra-stable beam steering to prevent unwanted excitations on neighboring atoms, a significant challenge as the number of qubits increases [5]. Furthermore, achieving the tight focus required for single-ion addressing is often made difficult by geometric constraints and restricted optical access [6,7]. These factors combine to make single-qubit addressing a major challenge in many experimental systems.One method of improving single-qubit addressing applies an auxiliary field gradient to shift qubit transition frequencies, affording a degree of selective control [8,9]. A similar technique uses an intense laser to introduce a position-dependent AC Stark shift [10,11]. Recently, quantum control has been used in conjunction with frequency shifts to achieve addressing with inhomogeneous control fields [12]. A recent proposal has also examined spatial refocusing through precise laser positioning coupled with controlled phase shifts [13]. These methods frequently require time-consuming calibrations to remove systematic errors while adding to experimental complexity, limiting scalability. These techniques also make strong physical assumptions of the nature of the qubit, and are generally not translatable to other qubit technologies.In this article we demonstrate an alternative control scheme that replaces simple single-qubit gates with a narrowband composite sequence of laser pulses designed for local addressing [14,15]. These sequences allow the exclusive manipulation of a single qubit even when neighboring qubits are subjected to significant laser intensity. Such compensating sequences reduce systematic control errors at the cost of increasing the time required to produce gates [15]. Our main result is a new technique to generate fully-compensating narrowband sequences using Lie-algebraic transformations of other known sequences. We use numerical minimization to identify sequences with superior error correction properties and low operation times compared to the original sequence family. Further, we demonstrate the effectiveness of these sequences ...

Time-resolved photon detection can be used to generate entanglement between distinguishable photons. This technique can be extended to entangle quantum memories that emit photons with different frequencies and identical temporal profiles without the loss of entanglement rate or fidelity. We experimentally realize this process using remotely trapped 171 Yb + ions where heralded entanglement is generated by interfering distinguishable photons. This technique may be necessary for future modular quantum systems and networks that are composed of heterogeneous qubits.PACS numbers: 03.67.Bg, 37.10.TyThe entanglement of remote quantum memories via photons is an enabling technology for modular quantum computing, transmission of quantum information, and networked quantum timekeeping [1][2][3][4][5]. All of these applications rely on the excellent control and long-lived coherence properties of quantum memories and the ease with which photons can be used to distribute both entanglement and quantum information.Currently, photon-mediated entanglement of remote quantum memories has only been achieved using heralded schemes; atomic ensembles [6], trapped ions [7], single neutral atoms in optical cavities [8], and nitrogen vacancy centers in diamond [9] have all been entangled in this manner. However, heralded entanglement is possible in these systems because the memories inherently emit indistinguishable photons or can be manipulated to do so. This requirement of photon indistinguishability is a major impediment to the construction of heterogeneous quantum networks and also hinders the entanglement of similar memories whose emission frequencies differ due to variations in local environment or fabrication. Recently, photons with frequencies that differ by many linewidths have been entangled using time-resolved detection and active feedforward [10]. Here, we extend this technique to entangle distinguishable remote quantum memories by interference of distinguishable photons.In order to generate heralded entanglement of remote quantum memories, photons emitted from each memory enter a partial Bell state analyzer where they interfere on a beamsplitter and are subsequently detected, projecting the memories into a corresponding entangled state. If the photons are identical, the memories will be projected into a known Bell state [11]. However, if the photons are distinguishable, the resulting entangled memory state will have some additional phase factor or unequal probability amplitudes. Here we assume that quantum memories labeled A and B emit photons with identical temporal profiles but frequencies that differ by ∆ω for a given polarization [12]. These two photons are detected within the Bell state analyzer a time ∆t apart, projecting the memories into a Bell state with a time-dependent phase, e.g.,), where {|0 ,|1 } are the computational basis states of each memory. The temporal resolution t r of the photon detection circuit determines how precisely the phase ∆ω∆t is known since the phase is probabilistically distributed over an in...

The masses of single molecular ions are nondestructively measured by cotrapping the ion of interest with a laser-cooled atomic ion, (40)Ca(+). Measurement of the resolved sidebands of a dipole forbidden transition on the atomic ion reveals the normal-mode frequencies of the two ion system. The mass of two molecular ions, (40)CaH(+) and (40)Ca(16)O(+), are then determined from the normal-mode frequencies. Isotopes of Ca(+) are used to determine the effects of stray electric fields on the normal mode measurement. The future use of resolved sideband experiments for molecular spectroscopy is also discussed.