  Trapped-ion qubits are a leading technology for practical quantum computing.
In this work, we present an architectural analysis of a linear-tape
architecture for trapped ions. In order to realize our study, we develop and
evaluate mapping and scheduling algorithms for this architecture.
  In particular, we introduce TILT, a linear "Turing-machine-like" architecture
with a multilaser control "head", where a linear chain of ions moves back and
forth under the laser head. We find that TILT can substantially reduce
communication as compared with comparable-sized Quantum Charge Coupled Device
(QCCD) architectures. We also develop two important scheduling heuristics for
TILT. The first heuristic reduces the number of swap operations by matching
data traveling in opposite directions into an "opposing swap", and also avoids
the maximum swap distance across the width of the head, as maximum swap
distances make scheduling multiple swaps in one head position difficult. The
second heuristic minimizes ion chain motion by scheduling the tape to the
position with the maximal executable operations for every movement. We provide
application performance results from our simulation, which suggest that TILT
can outperform QCCD in a range of NISQ applications in terms of success rate
(up to 4.35x and 1.95x on average). We also discuss using TILT as a building
block to extend existing scalable trapped-ion quantum computing proposals.
