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...
Despite the tremendous advances in laser cooling of neutral atoms and positive ions, no negatively charged ion has been directly laser cooled. The negative ion of lanthanum, La(-), has been proposed as the best candidate for laser cooling of any atomic anion [ and , Phys. Rev. A 81, 032503 (2010)]. Tunable infrared laser photodetachment spectroscopy is used to measure the bound-state structure of La(-), revealing a spectrum of unprecedented richness with multiple bound-bound electric dipole transitions. The potential laser-cooling transition ((3)F(2)(e)→(3)D(1)(o)) is identified and its excitation energy is measured. The results confirm that La^{-} is a very promising negative ion for laser-cooling applications.
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...
Trapped atomic ions are an ideal candidate for quantum network nodes, with long-lived identical qubit memories that can be locally entangled through their Coulomb interaction and remotely entangled through photonic channels. The integrity of this photonic interface is generally reliant on purity of single photons produced by the quantum memory. Here we demonstrate a singlephoton source for quantum networking based on a trapped 138 Ba + ion with a single photon purity of g 2 (0) = (8.1 ± 2.3) × 10 −5 without background subtraction. We further optimize the tradeoff between the photonic generation rate and the memory-photon entanglement fidelity for the case of polarization photonic qubits by tailoring the spatial mode of the collected light.
The performance of a quantum information processor depends on the precise control of phases introduced into the system during quantum gate operations. As the number of operations increases with the complexity of a computation, the phases of gates at different locations and different times must be controlled, which can be challenging for optically-driven operations. We circumvent this issue by demonstrating an entangling gate between two trapped atomic ions that is insensitive to the optical phases of the driving fields, while using a common master reference clock for all coherent qubit operations. Such techniques may be crucial for scaling to large quantum information processors in many physical platforms.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.