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Towards a measurement theory in QFT: "Impossible" quantum measurements are possible but not ideal
Quantum Physics · Submitted 22 Nov 2023
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim The non-relativistic solution shows that all nonlocal measurements are localizable (i.e., they can be carried out at a distance without violating no-signaling) but they (i) may require arbitrarily large entangled resources and (ii) cannot in general be ideal, i.e., are not immediately reproducible.
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The abstract, sentence by sentence
Naive attempts to put together relativity and quantum measurements lead to signaling between space-like separated regions. In QFT, these are known as impossible measurements. We show that the same problem arises in non-relativistic quantum physics, where joint nonlocal measurements (i.e., between systems kept spatially separated) in general lead to signaling, while one would expect no-signaling (based for instance on the principle of no-nonphysical communication). This raises the question: Which nonlocal quantum measurements are physically possible? We review and develop further a non-relativistic quantum information approach developed independently of the impossible measurements in QFT, and show that these two have been addressing virtually the same problem. The non-relativistic solution shows that all nonlocal measurements are localizable (i.e., they can be carried out at a distance without violating no-signaling) but they (i) may require arbitrarily large entangled resources and (ii) cannot in general be ideal, i.e., are not immediately reproducible. These considerations could help guide the development of a complete theory of measurement in QFT.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Naive attempts to put together relativity and quantum measurements lead to signaling between space-like separated regions. | background 1.00 | 0.07 | 0.03 | asserted 0.88 |
| s1 | In QFT, these are known as impossible measurements. | background 1.00 | 0.05 | 0.02 | asserted 1.00 |
| s2 | We show that the same problem arises in non-relativistic quantum physics, where joint nonlocal measurements (i.e., between systems kept spatially separated) in general lead to signaling, while one would expect no-signaling (based for instance on the principle of no-nonphysical communication). | result 0.75 | 0.64 | 0.07 | asserted 0.91 |
| s3 | This raises the question: Which nonlocal quantum measurements are physically possible? | gap 0.91 | 0.10 | 0.04 | unclear 0.83 |
| s4 | We review and develop further a non-relativistic quantum information approach developed independently of the impossible measurements in QFT, and show that these two have been addressing virtually the same problem. | contribution 0.87 | 0.78 | 0.06 | asserted 1.00 |
| s5 | The non-relativistic solution shows that all nonlocal measurements are localizable (i.e., they can be carried out at a distance without violating no-signaling) but they (i) may require arbitrarily large entangled resources and (ii) cannot in general be ideal, i.e., are not immediately reproducible. | result 0.98 | 0.61 | 0.85 | asserted 0.81 |
| s6 | These considerations could help guide the development of a complete theory of measurement in QFT. | future work 0.66 | 0.17 | 0.08 | hedged possibility 1.00 |
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Original abstract
Naive attempts to put together relativity and quantum measurements lead to signaling between space-like separated regions. In QFT, these are known as impossible measurements. We show that the same problem arises in non-relativistic quantum physics, where joint nonlocal measurements (i.e., between systems kept spatially separated) in general lead to signaling, while one would expect no-signaling (based for instance on the principle of no-nonphysical communication). This raises the question: Which nonlocal quantum measurements are physically possible? We review and develop further a non-relativistic quantum information approach developed independently of the impossible measurements in QFT, and show that these two have been addressing virtually the same problem. The non-relativistic solution shows that all nonlocal measurements are localizable (i.e., they can be carried out at a distance without violating no-signaling) but they (i) may require arbitrarily large entangled resources and (ii) cannot in general be ideal, i.e., are not immediately reproducible. These considerations could help guide the development of a complete theory of measurement in QFT.
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Cites as background 3 papers
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Sorkin's impossible measurements in QFT have recently received a great deal of attention, mostly thanks to a proposed solution that, at last, puts forward an explicit measurement scheme for QFT [ref] .
Measurement in Quantum Field Theory · Discussion and outlook · 0.87
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The problem of impossible measurements in QFT has gained interest in recent years (for a historical review, see [ref] ) and two main approaches have been proposed to solve this conundrum: The first one, pursued in Refs. [ref] , accepts that microcausality is not enough to single out the physical measurements and puts forward further constraints.
Eliminating the "impossible": Recent progress on local measurement theory for quantum field theory · Introduction · 0.97
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The Elegant Joint Measurement (EJM) is an observable whose eigenvectors form a basis of partially entangled states (all with the same degree of entanglement) with particular symmetry properties [ref] (see also [ref] for a classification of joint entangled measurements of two qubits).
Iso-entangled bases and joint measurements · Elegant Joint Measurements · 0.94
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