Relationship between a non-Hermitian Hamiltonian and its solution

In summary, the conversation discusses a non-Hermitian Hamiltonian that produces orthogonal solutions when accurate initial conditions are given. This is contrary to the expectation that non-Hermitian Hamiltonians only produce non-orthogonal solutions. The speaker also mentions that normal operators can be non-Hermitian and have orthogonal eigenvectors, but their corresponding eigenvalues are complex. The conversation ends with the speaker discussing their specific case of a complex and ill-conditioned matrix with orthogonal solutions that have both real and complex expectation values in their integrals.
  • #1
SeM
Hello, I Have a non-Hermitian Hamiltonian, which is defined as an ill-condition numbered complex matrix, with non-orthogonal elements and linearily independent vectors spanning an open subspace.

However, when accurate initial conditions are given to the ODE of the Hamiltoanian, it appears to give an orthogonal solution. Does that make sense? I would have thought that a non-Hermitian Hamiltonian gives only non-orthogonal solutions?

Thanks
 
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  • #2
SeM said:
I would have thought that a non-Hermitian Hamiltonian gives only non-orthogonal solutions?

Thanks
No, for example, normal operators are non-Hermitian. They have a complete set of orthogonal eigenvectors but the corresponding eigenvalues are complex and not real, in general.
In general, you can always do a singular value decomposition. It turns out that a matrix always has a set of orthogonal eigenvectors, but in general, these eigenvectors are not also eigenvectors of the transposed (or adjoint) matrix.
 
  • #3
Thanks Dr. Du! In my case, I have a complex matrix, which is not unitary and not normal, and is very ill-conditioned. However, its ODE are solved using some initial conditions, and orthogonal solutions are found. However the orthogonal solutions have both complex as well as real expectation values in their integrals:

\begin{equation}
\int_0^{2\pi} \psi \Omega \psi^*
\end{equation}
 

Related to Relationship between a non-Hermitian Hamiltonian and its solution

1. What is the difference between a non-Hermitian Hamiltonian and a Hermitian Hamiltonian?

A Hermitian Hamiltonian is a mathematical operator that describes the energy of a physical system. It is self-adjoint, meaning that it is equal to its own conjugate transpose. This results in real eigenvalues and orthogonality of eigenvectors. A non-Hermitian Hamiltonian, on the other hand, is not equal to its conjugate transpose and can have complex eigenvalues and non-orthogonal eigenvectors.

2. How does the non-Hermitian nature of a Hamiltonian affect its solution?

The non-Hermitian nature of a Hamiltonian can lead to non-orthogonal eigenvectors and complex eigenvalues. This can result in a non-unitary time evolution, meaning that the norm of the wavefunction may not be conserved. Additionally, the presence of complex eigenvalues can lead to non-exponential decay, making the time-evolution of the system more complicated.

3. Can a non-Hermitian Hamiltonian still have real eigenvalues?

Yes, it is possible for a non-Hermitian Hamiltonian to have real eigenvalues. This can occur when the Hamiltonian has a symmetry that ensures the reality of eigenvalues, such as PT-symmetry. In these cases, the non-Hermitian Hamiltonian can still behave similarly to a Hermitian Hamiltonian.

4. How do non-Hermitian Hamiltonians arise in physical systems?

Non-Hermitian Hamiltonians can arise in physical systems due to a variety of reasons. One common reason is the presence of open systems, where energy can be exchanged with the environment, leading to non-unitary time evolution. Non-Hermitian Hamiltonians can also arise due to the presence of external fields, such as electromagnetic fields, or due to the inclusion of dissipative or reactive terms in the Hamiltonian.

5. What implications does the non-Hermitian nature of a Hamiltonian have on quantum mechanics?

The non-Hermitian nature of a Hamiltonian can have several implications on quantum mechanics. It can lead to non-unitary time evolution, which can affect the conservation of energy and probability. It can also result in non-exponential decay and non-orthogonal eigenvectors, making the time-evolution of the system more complex. Additionally, the presence of complex eigenvalues can have an impact on the stability and dynamics of the system.

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