Minimally complex ion traps as modules for quantum communication and computing

Abstract

Optically linked ion traps are promising as components of network-based quantum technologies, including communication systems and modular computers. Experimental results achieved to date indicate that the fidelity of operations within each ion trap module will be far higher than the fidelity of operations involving the links; fortunately internal storage and processing can effectively upgrade the links through the process of purification. Here we perform the most detailed analysis to date on this purification task, using a protocol which is balanced to maximise fidelity while minimising the device complexity and the time cost of the process. Moreover we 'compile down' the quantum circuit to device-level operations including cooling and shuttling events. We find that a linear trap with only five ions (two of one species, three of another) can support our protocol while incorporating desirable features such as global control, i.e. laser control pulses need only target an entire zone rather than differentiating one ion from its neighbour. To evaluate the capabilities of such a module we consider its use both as a universal communications node for quantum key distribution, and as the basic repeating unit of a quantum computer. For the latter case we evaluate the threshold for fault tolerant quantum computing using the surface code, finding acceptable fidelities for the 'raw' entangling link as low as 83% (or under 75% if an additional ion is available).

High-Rate, High-Fidelity Entanglement of Qubits Across an Elementary Quantum Network

“…In this manuscript, we report the generation of entanglement between remote qubits at rates and fidelities approaching those of typical local operations, by swapping entanglement between photons emitted by the ions onto the ions themselves [24]. At these higher rates and fidelities, distillation procedures based on photonic entanglement [25] start to become a viable method for creating high quality entanglement across a scalable trapped ion quantum computer.…”

Certified Randomness From Steering Using Sequential Measurements

“…In particular, we will restrict to assuming we only have some noise in our state preparation, but all other parts of the device works perfectly. To do so, we test the state introduced in [22], which can be produced between two parties in a networked architecture of ion traps:…”

“…where φ + , φ − , ψ + , and ψ − are the standard 2-qubit Bell states. The state, (22), is a mixed state assuming uniform depolarising noise. In [22], this state is assumed to be one produced by two ion traps entangled by a photonic link.…”

“…The state, (22), is a mixed state assuming uniform depolarising noise. In [22], this state is assumed to be one produced by two ion traps entangled by a photonic link. The simple noise model is chosen to allow use of a technique to purify the state.…”

Dual-species, multi-qubit logic primitives for Ca+/Sr+ trapped-ion crystals

“…The Ca + /Sr + system has been considered recently for applications in QIP, though few quantum logic operations in the combined system have been reported. For instance, these species form the basis of several analyses of large-scale quantum computing platforms, both as sympathetic cooling ancillas [6] and for photon-emitting intermediaries in optically linked architectures [25]; a method has also been suggested to perform an interspecies gate in the Ca + /Sr + system using a single laser wavelength [23]. While considerable work demonstrating same-species, two-qubit operations in Ca + [18,[26][27][28][29], and to a lesser extent Sr + [19,30], exists, their use together has not been investigated widely.…”