Since this is a one-liner, you might want to shorten it a bit. Please note that a method call without invocant will be invoked with $_.

So you could change:

my @F=$_.split("\t");
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to

my @F= .split("\t");
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Similarly you appear to be printing the whole line. So, rather than:

{@F.join("\t").say}
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you could have:

{.say}
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I think that Anonymous Monk's original suggestion would have re-read the patternFile on every line which would be inefficient.

Probably not. A state variable is initialized only once. From the documentation (https://docs.perl6.org/syntax/state):

However, initialization happens exactly once the first time the initialization is encountered in the normal flow of execution. Thus, state variables will retain their value across multiple executions of the enclosing block or routine.

But this should probably be confirmed with a test.

Update: added the word "variable" which was missing in one sentence ("A state variable ...")