Feat/bumper

[Katie1harrison]

Add bumper attributes to the unitary data type

Summary

support for assigning bumper-level constraints to the unitary data type.

The new syntax introduces two attributes:

• bumper – specifies the exact number of bumper levels.
• bumper_max – specifies the maximum number of bumper levels the compiler may use.

note that setting bumper levels to a value does not retrospectively change the input unitary. rather we want both the unitary and bumper level information to be stored and accessed at compilation.####

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Motivation

When compiling a target unitary into bosonic operations, the compiler may use additional bumper states during decomposition. This PR adds language support for allowing users to specify these constraints directly on a unitary.

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Supported Grammar

Automatic bumper selection

If no bumper attribute is specified, the compiler is free to choose the number of bumper levels.

unitary u;

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Exact bumper count

unitary u;
u.bumper = 4;

Meaning:

• The compiler must use exactly 4 bumper levels.

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Maximum bumper count

unitary u;
u.bumper_max = 3;

Meaning:

• The compiler may use 0–3 bumper levels.

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Valid Examples

Exact bumper count

unitary u;
u.bumper = 4;

Maximum bumper count

unitary u;
u.bumper_max = 3;

Reassigning the bumper count

unitary u;

u.bumper = 4;
u.bumper = 2;

Incrementing the bumper count

unitary u;

u.bumper = 4;
u.bumper += 2;

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Invalid Examples

Attribute before declaration

u.bumper = 4;

Missing value

unitary u;
u.bumper =;

Missing assignment operator

unitary u;
u.bumper 4;

Missing unitary identifier

unitary u;
.bumper = 4;

Attribute inside the declaration

unitary u.bumper = 4;

Instead use

unitary u;
u.bumper = 4;

Attribute on another data type

qubit q;
q.bumper = 4;

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Implementation

This PR extends the parser to recognize unitary attribute assignments of the form

Identifier "." Identifier AssignmentOperator Expression ";"

For example,

u.bumper = 4;

is parsed as

• Unitary identifier: u
• Attribute: bumper
• Assignment operator: =
• Expression: 4

The same grammar also supports

u.bumper += 2;

and

u.bumper_max = 3;

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Design Decisions

bumper and bumper_max are identifiers

Rather than introducing new lexer keywords, both bumper and bumper_max are parsed as identifiers following the . operator.

For example,

u.bumper = 4;

Attributes are separate statements

Attributes are assigned after a unitary declaration.

unitary u;
u.bumper = 4;

rather than

unitary u.bumper = 4;

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