|
| related topics |
| {qubit, qubits, gate} |
| {time, systems, information} |
| {let, theorem, proof} |
| {state, phys, rev} |
| {algorithm, log, probability} |
| {entanglement, phys, rev} |
| {wave, scattering, interference} |
| {measurement, state, measurements} |
|
Remarks on Universal Quantum Computer
Yu Shi
abstract: According to Deutsch, a universal quantum Turing machine (UQTM) is able to
perform, in repeating a fixed unitary transformation on the total system, an
arbitrary unitary transformation on an arbitrary data state, by including a
program as another part of the input state. We note that if such a UQTM really
exists, with the program state dependent on the data state, and if the
prescribed halting scheme is indeed valid, then there would be no entanglement
between the halt qubit and other qubits, as pointed out by Myers. If, however,
the program is required to be independent of the data, the concerned
entanglement appears, and is problematic no matter whether the halt qubit is
monitored or not. We also note that for a deterministic programmable quantum
gate array, as discussed by Nielson and Chuang, if the program is allowed to
depend on the data state, then its existence has not been ruled out. On the
other hand, if UQTM exists, it can be simulated by repeating the operation of a
fixed gate array. However, more importantly, we observe that it is actually
still open whether Deutsch's UQTM exists and whether a crucial concatenation
scheme, of which the halting scheme is a special case, is valid.
- oai_identifier:
- oai:arXiv.org:quant-ph/9908074
- categories:
- quant-ph
- comments:
- revtex, 14 pages, version appearing in Phys. Lett. A
- doi:
- 10.1016/S0375-9601(02)00015-4
- arxiv_id:
- quant-ph/9908074
- journal_ref:
- Phys. Lett. A 293 (2002) 277
- created:
- 1999-08-24
- updated:
- 2002-01-20
Full article ▸
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