System-based extension of qEOM algorithm for quantum computation of excited-state properties

1. A system, comprising:

a classical processor that executes the following computer executable components stored in memory, wherein the computer executable components comprise:

a mapping component that maps Hamiltonian and pairs of excitation operators and respective adjoints to qubit operators to facilitate measurement on quantum hardware; and

a computation component that computes matrix operators in terms of commutators between the qubit operators and the facilitated measurements on the quantum hardware, wherein the commutators are computed utilizing symbolic calculus.

2. The system of claim 1 , wherein the mapping component maps the computed commutator onto a first qubit operator.

3. The system of claim 1 , wherein the computation component computes the matrix operators to define matrices: M, Q, V and W that are parallelized across two or more computer processing units (CPUs).

4. The system of claim 1 , wherein the computation component employs a class-based Python library to facilitate analytically computing the commutators.

5. The system of claim 4 , wherein the computation component utilizes an operatorstring object corresponding to expression:

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6. The system of claim 5 , wherein the operatorstring is equipped with methods for multiplication, contraction of tensors T, Wick's decomposition {circumflex over (φ)} i 1 . . . {circumflex over (φ)} i n= N [{circumflex over (φ)} i 1 . . . {circumflex over (φ)} i n ]+Σ ij N [{circumflex over (φ)} i 1 . . . {circumflex over (φ)} i . . . {circumflex over (φ)} j . . . {circumflex over (φ)} i n ]+Σ ijkl N [{circumflex over (φ)} i 1 . . . {circumflex over (φ)} i . . . {circumflex over (φ)} k . . . {circumflex over (φ)} j . . . {circumflex over (φ)} l . . . {circumflex over (φ)} i n ]+ . . . wherein bars denote contraction and N denotes normal ordering and algebraic simplification.

7. The system of claim 1 , wherein the computation component generates estimators of excited-state properties, considering constants of motion and non-constants of motion to facilitate quantitatively describing phenomena.

8. The system of claim 7 , wherein the constants of motion comprise spin, and the non-constants of motion comprise at least one of: dipoles or density matrices.

9. The system of claim 7 , wherein the computation component quantitatively describes at least one of the following phenomena: single-triplet excitations or electronic states of fragments in the dissociation of a molecule.

10. The system of claim 8 , wherein the computation component generates estimators of constants of motion X, spin squared, wherein X is a constant of motion and c a string of vectors describing an excited state, then

(

M

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M

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c

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X

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V

W

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W

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V

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c

,

wherein {tilde over (M)} ij = ψ|[E i + , X, E j ]|ψ , {tilde over (Q)} ij =− ψ|[E i + , X, E j + ]|ψ , V ij = ψ|[E i + , E j ]|ψ , W ij =− ψ|[E i + , E j + ]|ψ , and wherein the computation component computes difference ΔX between a value taken by X on an excited state and on a ground state by evaluating additional matrix elements.

11. The system of claim 1 , wherein the computation component diagnoses excited-state properties by quantifying physical properties of transition from a ground state to a target excited state.

12. The system of claim 10 , wherein the computation component for observables X that are not constants of motion, transition and excited-states matrix elements are evaluated introducing additional quantum measurements of the form Ψ i |X|Ψ j = Ψ 0 |E i + XE j |Ψ 0 =Σ μ c μ (X, ij) Ψ 0 |P μ |Ψ 0 .

13. The system of claim 12 , wherein the computation component makes accessible transition and excited-state one-body density matrices and dipole moments.

14. The system of claim 10 , wherein the computation component:

(a) utilizes quantum hardware to measure matrices, V, W, M, Q, {tilde over (M)}, {tilde over (Q)};

(b) utilizes classical hardware to determine E, ΔX, and c;

(c) measures operators E j + E j E i + XE j , using quantum hardware; and

(d) determines transition reduced density matrices (RDMs) and non-constants of motion (COMs) using classical hardware.

15. A computer-implemented method, comprising:

mapping, using a mapping component, Hamiltonian and pairs of excitation operators and respective adjoints to qubit operators to facilitate measurement on quantum hardware; and

computing, using a computation component, matrix operators in terms of commutators between the qubit operators and the facilitated measurements on the quantum hardware, wherein the commutators are computed utilizing symbolic calculus.

16. The method of claim 15 , wherein the mapping comprises mapping the computed commutator onto a first qubit operator.

17. The method of claim 15 , further comprising computing, using the computing component, the matrix operators to define matrices: M, Q, V and W that are parallelized across two or more computer processing units (CPUs).

18. The method of claim 15 , further comprises employing, using the computation component, a class-based Python library to facilitate analytically computing the commutators.

19. The method of claim 18 , further comprises utilizing, using the computation component, an operatorstring object corresponding to expression:

X

=

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T

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1

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wherein the operatorstring is equipped with methods for multiplication, contraction of tensors T, Wick's decomposition {circumflex over (φ)} i 1 . . . {circumflex over (φ)} i n= N [{circumflex over (φ)} i 1 . . . {circumflex over (φ)} i n ]+Σ ij N [{circumflex over (φ)} i 1 . . . {circumflex over (φ)} i . . . {circumflex over (φ)} j . . . {circumflex over (φ)} i n ]+Σ ijkl N [{circumflex over (φ)} i 1 . . . {circumflex over (φ)} i . . . {circumflex over (φ)} k . . . {circumflex over (φ)} j . . . {circumflex over (φ)} l . . . {circumflex over (φ)} i n ]+ . . . wherein bars denote contraction and N denotes normal ordering and algebraic simplification.

20. The method of claim 19 , further comprising generating, using the computation component, estimators of constants of motion X, spin squared, wherein X is a constant of motion and c a string of vectors describing an excited state, then

(

M

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Q

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Q

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M

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)

⁢

c

=

Δ

⁢

X

⁡

(

V

W

-

W

*

-

V

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)

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c

,

wherein {tilde over (M)} ij = ψ|[E i + , X, E j ]|ψ , {tilde over (Q)} ij =− ψ|[E i + , X, E j + ]|ψ , V ij = ψ|[E i + , E j ]|ψ , W ij =− ψ|[E i + , E j + ]|ψ , and wherein the computation component computes difference ΔX between a value employed by X on an excited state and on a ground state by evaluating additional matrix elements, and wherein the computation component for observables X that are not constants of motion, transition and excited-states matrix elements are evaluated introducing additional quantum measurements of the form Ψ i |X|Ψ j = Ψ 0 |E i + XE j |Ψ 0 =Σ μ c μ (X, ij) Ψ 0 |P μ |Ψ 0 .

21. The method of claim 20 , further comprises:

(a) utilizing quantum hardware to measure matrices, V, W, M, Q, {tilde over (M)}, {tilde over (Q)};

(b) utilizing classical hardware to determine E, ΔX, and c;

(c) measuring operators E i + E j E i + XE j , using quantum hardware; and

(d) determining transition reduced density matrices (RDMs) and non-constants of motion (COMs) using classical hardware.

22. A computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a classical processor to cause the classical processor to:

map Hamiltonian and pairs of excitation operators and respective adjoints to qubit operators to facilitate measurement on quantum hardware; and

compute matrix operators in terms of commutators between the qubit operators and the facilitated measurements on the quantum hardware, wherein the commutators are computed utilizing symbolic calculus.

23. The computer program product of claim 22 , the program instructions further executable by a classical processor to cause the processor to:

(a) map the computed commutator onto a first qubit operator;

(b) compute the matrix operators to define matrices: M, Q, V and W that are parallelized across two or more computer processing units (CPUs);

(c) utilize an operatorstring object corresponding to expression:

X

=

γ

⁢

⁢

T

i

a

1

⁢

⁢

…

⁢

⁢

i

a

k

⁢

ϕ

^

i

1

⁢

⁢

…

⁢

⁢

ϕ

^

i

n

,

wherein the operatorstring is equipped with methods for multiplication, contraction of tensors T, Wick's decomposition {circumflex over (φ)} i 1 . . . {circumflex over (φ)} i n= N [{circumflex over (φ)} i 1 . . . {circumflex over (φ)} i n ]+Σ ij N [{circumflex over (φ)} i 1 . . . {circumflex over (φ)} i . . . {circumflex over (φ)} j . . . {circumflex over (φ)} i n ]+Σ ijkl N [{circumflex over (φ)} i 1 . . . {circumflex over (φ)} i . . . {circumflex over (φ)} k . . . {circumflex over (φ)} j . . . {circumflex over (φ)} l . . . {circumflex over (φ)} i n ]+ . . . wherein bars denote contraction and N denotes normal ordering and algebraic simplification;

(d) generate estimators of constants of motion X, spin squared, wherein X is a constant of motion and c a string of vectors describing an excited state, then

(

M

~

Q

~

Q

~

*

M

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)

⁢

c

=

Δ

⁢

X

⁡

(

V

W

-

W

*

-

V

*

)

⁢

c

,

wherein {tilde over (M)} ij = ψ|[E i + , X, E j ]|ψ , {tilde over (Q)} ij =− ψ|[E i + , X, E j + ]|ψ , V ij = ψ|[E i + , E j ]|ψ , W ij =− ψ|[E i + , E j + ]|ψ , and wherein the computation component computes difference ΔX between a value employed by X on an excited state and on a ground state by evaluating additional matrix elements, and for observables X that are not constants of motion, transition and excited-states matrix elements are evaluated introducing additional quantum measurements of the form Ψ i |X|Ψ j = Ψ 0 |E i + XE j |Ψ 0 =Σ μ c μ (X, ij) Ψ 0 |P μ |Ψ 0 .