Returns the complex amplitude vector of the ZZFeatureMap quantum
state \(\lvert\phi(\mathbf{x})\rangle\) produced by the data-
encoding circuit of Havlicek et al. (2019). The feature vector
x should already be normalised into the range [0, pi] — see
quantum_scale().
Usage
quantum_feature_map(x, reps = 2L)
Arguments
- x
Numeric vector of features (one qubit per feature).
- reps
Integer, number of times the encoding circuit is
repeated (>= 1). Higher values give more expressive kernels at
a per-sample simulation cost of O(reps * 2^n).
Value
Complex vector of length 2^length(x) — the state-vector
amplitudes of \(\lvert\phi(\mathbf{x})\rangle\) in the
computational basis.
Examples
psi <- quantum_feature_map(c(pi/4, pi/3, pi/2), reps = 2L)
sum(Mod(psi)^2) # 1 — quantum state is normalised
#> [1] 1
