The theory of PT-symmetry describes the non-hermitian Hamiltonian with real energy levels, which means that the Hamiltonian
His invariant neither under parity operator
P, nor under time reversal operator
T,
PTH=
H. Whether the Hamiltonian is real and symmetric is not a necessary condition for ensuring the fundamental axioms of quantum mechanics: real energy levels and unitary time evolution. The theory of PT-symmetry plays a significant role in studying quantum physics and quantum information science, Researchers have paid much attention to how to describe PT-symmetry of Hamiltonian. In the paper, we define operator
Faccording to the PT-symmetry theory and the normalized eigenfunction of Hamiltonian. Then we first describe the PT-symmetry of Hamiltonian in dimensionless cases after finding the features of commutator and anti-commutator of operator
CPTand operator
F. Furthermore, we find that this method can also quantify the PT-symmetry of Hamiltonian in dimensionless case.
I(
CPT,
F) = ||[
CPT,
F]||
CPTrepresents the part of PT-symmetry broken, and
J(
CPT,
F) = ||[
CPT,
F]||
CPTrepresents the part of PT-symmetry. If
I(
CPT,
F) = ||[
CPT,
F]||
CPT= 0, Hamiltonian
His globally PT-symmetric. Once
I(
CPT,
F) = ||[
CPT,
F]||
CPT≠ 0, Hamiltonian
His PT-symmetrically broken. In addition, we propose another method to describe PT-symmetry of Hamiltonian based on real and imaginary parts of eigenvalues of Hamiltonian, to judge whether the Hamiltonian is PT symmetric. Re
F= 1/4||(
CPTF+
F)||CPT represents the sum of squares of real part of the eigenvalue
Enof Hamiltonian
H, Im
F= 1/4||(
CPTF–
F)||CPT is the sum of imaginary part of the eigenvalue
Enof a Hamiltonian
H. If Im
F= 0, Hamiltonian
His globally PT-symmetric. Once Im
F≠ 0, Hamiltonian
His PT-symmetrically broken. Re
F= 0 implies that Hamiltonian
His PT-asymmetric, but it is a sufficient condition, not necessary condition. The later is easier to realize in the experiment, but the studying conditions are tighter, and it further requires that
CPT
$\phi_n $
(
x) =
$\phi_n $
(
x). If we only pay attention to whether PT-symmetry is broken, it is simpler to use the latter method. The former method is perhaps better to quantify the PT-symmetrically broken part and the part of local PT-symmetry.