1 files changed, 49 insertions, 0 deletions
diff --git a/tester/noise.c b/tester/noise.c
new file mode 100644
index 0000000..df791ae
--- /dev/null
+++ b/tester/noise.c
@@ -0,0 +1,49 @@
+#include "tests.h"
+
+#include <math.h>
+
+void run_noise_tests(void)
+{
+	psi_test_section("Noise channels");
+
+	struct PsiDensityMatrix pure = psi_new_density_matrix(1);
+	psi_test_check(psi_is_pure_density_matrix(pure, 1e-10), "fresh density matrix is pure");
+	psi_test_check(fabs(psi_trace_density_matrix(pure).real - 1.0) < 1e-10, "trace = 1");
+	psi_free_density_matrix(&pure);
+
+	struct PsiDensityMatrix bf = psi_new_density_matrix(1);
+	struct PsiNoiseChannel flip = psi_bit_flip_channel(0.25);
+	psi_apply_noise_channel(&bf, flip, 0);
+	double probs[2];
+	psi_density_matrix_probabilities(bf, probs);
+	psi_test_check(fabs(probs[0] - 0.75) < 1e-10 && fabs(probs[1] - 0.25) < 1e-10,
+	               "bit_flip(0.25) on |0>: p = [0.75, 0.25]");
+	psi_test_check(fabs(psi_purity_density_matrix(bf) - 0.625) < 1e-10,
+	               "bit_flip(0.25) purity = 0.625");
+	psi_free_noise_channel(&flip);
+	psi_free_density_matrix(&bf);
+
+	struct PsiComplex one[2] = { psi_new_complex(0.0, 0.0), psi_new_complex(1.0, 0.0) };
+	struct PsiDensityMatrix damp = psi_new_density_matrix_from_state(one, 2);
+	struct PsiNoiseChannel ad = psi_amplitude_damping_channel(1.0);
+	psi_apply_noise_channel(&damp, ad, 0);
+	double dprobs[2];
+	psi_density_matrix_probabilities(damp, dprobs);
+	psi_test_check(fabs(dprobs[0] - 1.0) < 1e-10, "amplitude_damping(1.0) fully decays |1> -> |0>");
+	psi_free_noise_channel(&ad);
+	psi_free_density_matrix(&damp);
+
+	struct PsiComplex zero[2] = { psi_new_complex(1.0, 0.0), psi_new_complex(0.0, 0.0) };
+	struct PsiDensityMatrix fid = psi_new_density_matrix_from_state(zero, 2);
+	psi_test_check(fabs(psi_fidelity_density_matrix(fid, zero) - 1.0) < 1e-10,
+	               "fidelity(|0><0|, |0>) = 1");
+	psi_free_density_matrix(&fid);
+
+	struct PsiDensityMatrix depo = psi_new_density_matrix(1);
+	struct PsiNoiseChannel dc = psi_depolarising_channel(0.3);
+	psi_apply_noise_channel(&depo, dc, 0);
+	psi_test_check(fabs(psi_trace_density_matrix(depo).real - 1.0) < 1e-10,
+	               "depolarising preserves trace");
+	psi_free_noise_channel(&dc);
+	psi_free_density_matrix(&depo);
+}