Deferred timing resolution using stretch
Overview: what is stretch and why is it useful?
Example
Example of using stretch in a dynamic circuit
Limitations
The following constraints apply when using stretch:
-
At most one stretch variable per qubit set between barriers (implicit and explicit). A qubit set is one or more qubits; these sets must be mutually exclusive. Valid:
stretch a; stretch b; delay[a] $0, $1; delay[b] $2Invalid:
stretch a; stretch b; delay[a] $0, $1; delay[b] $0; -
A stretch variable cannot be used between multiple sets of barriers. Valid:
barrier $0, $1; delay[a] $0; barrier $3; delay[a] $0; barrier $0, $1;Invalid:
barrier $0, $1; delay[a] $0; barrier $0, $1; delay[a] $0; barrier $0, $1; -
Stretch expressions are limited to those of the form
A*stretch + BwhereAandBare floating point or integer constants. Valid:delay[2 * a + 3.0] $0; delay[a / 5 - 40.0] $0; delay[a + a] $0; # equivalent to "delay[2 * a] $0;"Invalid:
delay[2 * a * a] $0; -
Stretch expressions can only include a single stretch variable. Invalid:
stretch a;stretch b; delay[ a + b ] $0;delay[ a * b ] $0; -
Stretch expressions cannot resolve to negative delay values. Invalid:
delay[a - 40.0] $0; #if "a" resolves to a value <= 40.0 -
Any remainder resulting from a stretch resolution is added to the first delay that uses the stretch. Example:
stretch a; barrier $0, $1; delay[100dt] $0; delay[a] $1; # resolves to 26 x $1; # duration: 8 delay[a] $1; # resolves to 25 x $1; # duration: 8 delay[a] $1; # resolves to 25 x $1; # duration: 8 barrier $0, $1;The above code resolves to a value of 25 with a remainder of 1. The first delay
[a]will have the remainder added.Stretch resolution equation: