Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Improved entanglement detection with subspace witnesses   Entanglement, while being critical in many quantum applications, is difficult
to characterize experimentally. While entanglement witnesses based on the
fidelity to the target entangled state are efficient detectors of entanglement,
they in general underestimate the amount of entanglement due to errors during
state preparation and measurement. Therefore, to detect entanglement more
robustly in the presence of such control errors, we introduce a 'subspace'
witness that detects a broader class of entangled states with strictly larger
violation than the conventional state-fidelity witness at the cost of
additional measurements, while remaining more efficient with respect to state
tomography. We experimentally demonstrate the advantages of the subspace
witness by generating and detecting entanglement with a hybrid, two-qubit
system composed of electronic spins in diamond. We further extend the notion of
subspace witness to specific genuine multipartite entangled (GME) states such
as GHZ, W, and Dicke states, and motivate the choice of the metric based on
quantum information tasks such as entanglement-enhanced sensing. In addition,
as the subspace witness identifies the many-body coherences of the target
entangled state, it facilitates (beyond detection) lower-bound quantification
of entanglement via generalized concurrences. We expect the straightforward and
efficient implementation of subspace witnesses would be beneficial in detecting
specific GME states in noisy, intermediate-scale quantum processors with a
hundred qubits.

25
The categories of this paper are: patt-sol
7
The categories of this paper are: hep-th
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph