  The control over quantum states in atomic systems has led to the most precise
optical atomic clocks to date. Their sensitivity is currently bounded by the
standard quantum limit, a fundamental floor set by quantum mechanics for
uncorrelated particles, which can nevertheless be overcome when operated with
entangled particles. Yet demonstrating a quantum advantage in real world
sensors is extremely challenging and remains to be achieved aside from two
remarkable examples, LIGO and more recently HAYSTAC. Here we illustrate a
pathway for harnessing scalable entanglement in an optical transition using 1D
chains of up to 51 ions with state-dependent interactions that decay as a
power-law function of the ion separation. We show our sensor can be made to
behave as a one-axis-twisting (OAT) model, an iconic fully connected model
known to generate scalable squeezing. The collective nature of the state
manifests itself in the preservation of the total transverse magnetization, the
reduced growth of finite momentum spin-wave excitations, the generation of spin
squeezing comparable to OAT (a Wineland parameter of $-3.9 \pm 0.3$ dB for only
N = 12 ions) and the development of non-Gaussian states in the form of atomic
multi-headed cat states in the Q-distribution. The simplicity of our protocol
enables scalability to large arrays with minimal overhead, opening the door to
advances in timekeeping as well as new methods for preserving coherence in
quantum simulation and computation. We demonstrate this in a Ramsey-type
interferometer, where we reduce the measurement uncertainty by $-3.2 \pm 0.5$
dB below the standard quantum limit for N = 51 ions.
