On 07-04-2022 02:36, Brent Meeker wrote:
On 4/6/2022 5:23 PM, smitra wrote:
On 07-04-2022 00:58, Bruce Kellett wrote:
On Thu, Apr 7, 2022 at 8:22 AM smitra <smi...@zonnet.nl> wrote:
On 06-04-2022 13:35, Bruce Kellett wrote:
I agree. Entanglement is a distinctively quantum phenomenon and
cannot
be simulated classically. But that does not mean that using a
quantum
computer will necessarily enable you to simulate a Bell
experiment.
The quantum computer operates essentially by classical logic. So
unless you somehow generate a quantum entanglement (outside of the
necessary entanglement for the operation of the computer's
qubits),
you are not going to be able to simulate a Bell entangled state,
even
on a quantum computer.
You can't do it "from the outside" but you can consider observers
simulated by a quantum computer.
But then you have the problem of whether "observers" simulated by a
quantum computer can actually make measurements. The essence of a
measurement is the formation of permanent records in the environment.
It's perfectly possible for an observer to make an observation without
there being any permanent record. The physical processes that makes
someone be able to see and feel something has noting to do with the
formation of permanent records.
But it has everything to do with seeing and feeling something
definite...not a superposition.
What is needed is to get to an unambiguous mathematical formalism that
describes an observation. How to write a state as a superposition of
states corresponding to definite observations then follows from that.
One would then then expect that for macroscopic observers like us, this
will mean that definite observations will exist in stable sectors where
there are to some good approximation, permanent records. But defining
observations using this property is doing things backward, it's
something that should (at least in principle) be explained by the
theory.
In general, it's wrong for a fundamental theory to rely on effective
macroscopic concepts for formulating fundamental concepts that are used
to define that theory.
Quantum computers cannot do this unless they stop and print out a
result. Your quantum computer simulation requires a redefinition of
the concept of measurement so that it becomes essentially
meaningless.
It forces one to come up with a more reasonable definition of
measurement. If I observe something, then that's because there is a
brain that's running the algorithm that corresponds to that
observation. In the context of the MWI one then needs to assume that
there exists algorithms for observations made by Alice and Bob which
then defines the required preferred basis.
And a what "preferred" means is that the observation produces
eigenvalues and eigenvectors in that basis.
Yes, so, if we consider a particular experimental setup then that
defines observables. In he MWI where everything happens due to the
evolution of the Schrödinger equation, and every bit of information an
observer accumulates is then both due to unitary time evolution and is
also a quantum measurement, one is then led to a preferred basis in the
form of the algorithm that describes the observer. If an observer uses a
measurement device, you can lump that device and the system being
measured together with the observer and call that a generalized
observer. So, in general one should think of the complete set of
commuting observables as specifying a generalized observer.
Saibal
Brent
Saibal
Bruce
The dynamics of a quantum computer is
manifestly local and unitary, so it provides for a transparent
argument.
Saibal
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