QubitizationWalkOperator add attribute: sum of LCU coefficients
#890
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| @@ -64,6 +67,7 @@ class QubitizationWalkOperator(GateWithRegisters): | |||
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| select: SelectOracle | |||
| prepare: PrepareOracle | |||
| sum_of_ham_coeffs: Optional[float] | |||
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The default value here should be 1 or something else?
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I didn't set a default to avoid accidentally forgetting it while building walk ops
But as the sum_of_ham_coeffs attribute is not needed in the decomposition/call-graph, it won't break anything. It's only needed for Hamiltonian simulation, in which case it needs to be correctly calculated anyway.
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right, I think Optional[float] = None in that case.
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would it be better to not have a default, and let the user explicitly specify None when they don't know the value? (just to make sure it's not accidentally omitted)
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It's typically called lambda in the literature which is problematic in python as a variable name I know. Maybe sum_of_lcu_coeffs? |
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Is |
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Yes I think that makes sense. That way we can also implicitly compute this value because we usually pass the exact coeffs to Prepare (which are normalized there). For ex. it would simplify this (we can drop L93) Qualtran/qualtran/bloqs/chemistry/ising/hamiltonian.py Lines 92 to 94 in 91b80b1 |
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@tanujkhattar PTAL |
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| @@ -92,6 +94,11 @@ def signature(self) -> Signature: | |||
| def reflect(self) -> ReflectionUsingPrepare: | |||
| return ReflectionUsingPrepare(self.prepare, control_val=self.control_val, global_phase=-1) | |||
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| @cached_property | |||
| def sum_of_lcu_coefficients(self) -> Optional[float]: | |||
| r"""value of $\lambda$, i.e. sum of the coefficients $w_l$.""" | |||
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Let's clarify by writing "sum of absolute values of coefficients. " instead. In this case, the docstring of the class does clarify that each
qualtran/bloqs/select_and_prepare.py
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| a selection register $|i\rangle$. In order to prepare such a state, the PREPARE circuit is also | ||
| allowed to use a junk register that is entangled with selection register. | ||
| the coefficients as amplitudes of a state $|\Psi\rangle = \sum_{i=0}^{N-1} \sqrt{\frac{c_{i}}{\lambda}} |i\rangle$ | ||
| where $\lambda = \sum_i c_i$, using a selection register $|i\rangle$. In order to prepare such |
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| where $\lambda = \sum_i c_i$, using a selection register $|i\rangle$. In order to prepare such | |
| where $\lambda = \sum_i | c_i |$, using a selection register $|i\rangle$. In order to prepare such |
qualtran/bloqs/select_and_prepare.py
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| @property | ||
| def l1_norm_of_coeffs(self) -> Optional['SymbolicFloat']: | ||
| r"""Sum of the coefficients $c_i$. |
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| r"""Sum of the coefficients $c_i$. | |
| r"""Sum of the absolute values of coefficients $c_i$. |
fixes #868
The sum of coefficients determines the complexity of hamiltonian simulation. This will also enable us to propagate symbolic values to the prepare gate.
@tanujkhattar could you review this? Also it would be great if someone with qchem expertise checks whether the sum of coeffs for the Hubbard gate is correct.