High-Fidelity Trapped-Ion Quantum Logic Using Near-Field Microwaves

Abstract

We demonstrate a two-qubit logic gate driven by near-field microwaves in a room-temperature microfabricated surface ion trap. We introduce a dynamically decoupled gate method, which stabilizes the qubits against fluctuating energy shifts and avoids the need to null the microwave field. We use the gate to produce a Bell state with fidelity 99.7(1)%, after accounting for state preparation and measurement errors. The gate is applied directly to ^{43}Ca^{+} hyperfine "atomic clock" qubits (coherence time T_{2}^{*}≈50 s) using the oscillating magnetic field gradient produced by an integrated microwave electrode.

Quantum dynamics of trapped ions in a dynamic field gradient using dressed states

“…In the main text of this article, we concentrate on conditional multi-qubit gates described by H J equation (10), which is directly induced by a single static or resonant dynamic gradient field. However, also Mølmer-Sørensen like gates [22] can be performed with MAGIC [11,17,25,38,39] with and without dressed states. In this section, we discuss some possibilities of carrying out Mølmer-Sørensen-type gates in the dressed-state picture of dynamic MAGIC.…”

“…In current experiments where a dynamic gradient field is applied, great care is taken to null the dynamic magnetic field at the ions' positions and thus to retain only a gradient of the dynamic field at this position [13,28,29] in order to obtain high-fidelity two-qubit gates. Another approach is to use an extra dressing field to reduce errors resulting from a non-zero offset field [25]. Here, we show how atomic states dressed by the dynamic magnetic gradient field itself could be employed for conditional quantum gates, thus decisively simplifying experimental efforts necessary when implementing the dynamic MAGIC scheme.…”

“…Using a static field gradient, a quantum byte (eight ions) could be addressed with a measured cross-talk between closely spaced, interacting ions in the 10 −5 range [20]. MAGIC was also employed to demonstrate two-qubit gates [13,14,17,25], three-qubit gates [26], and opens new possibilities for quantum simulations and quantum computation [26,27].…”

High-Fidelity Preservation of Quantum Information During Trapped-Ion Transport

“…These building blocks include single qubit rotation [9,10], individual addressing of interacting ions [11], and internal state detection [12]. In addition, high fidelity twoqubit quantum gates [10,[13][14][15][16] and coherent three-qubit conditional quantum gates [17,18] have been implemented.Straightforward scaling up to an arbitrary size of a single ion trap quantum register, at present, appears unlikely to be successful because the growing size of a single register usually introduces additional constraints imposed by the confining potential and by the Coulomb interaction of ion strings [19]. Even though, for instance, transverse modes and anharmonic trapping [20] may be employed for conditional quantum logic, a general claim might be that, at some point it is useful to divide a single ion register into subsystems and to exchange quantum information between these subsystems [2][3][4][5].…”

“…These building blocks include single qubit rotation [9,10], individual addressing of interacting ions [11], and internal state detection [12]. In addition, high fidelity twoqubit quantum gates [10,[13][14][15][16] and coherent three-qubit conditional quantum gates [17,18] have been implemented.…”