Abstract.
We study effects of static inter-qubit interactions on the stability of the Grover quantum search algorithm. Our numerical and analytical results show existence of regular and chaotic phases depending on the imperfection strength \(\varepsilon\). The critical border \(\varepsilon_c\) between two phases drops polynomially with the number of qubits n q as \(\varepsilon_c \sim n_q^{-3/2}\). In the regular phase \((\varepsilon < \varepsilon_c)\) the algorithm remains robust against imperfections showing the efficiency gain \(\varepsilon_c / \varepsilon\) for \(\varepsilon \gtrsim 2^{-n_q/2}\). In the chaotic phase \((\varepsilon > \varepsilon_c)\) the algorithm is completely destroyed.
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Here we consider only the subspace ([3]), a small probability leakage to all other states is not crucial since it will be randomly distributed over 2N−4 states
Some improvement can be reached in this situation if to perform measurements after a shorter number of iterations given by a typical decay time \(t_{dec} \sim 1/(\varepsilon^2 n_g) \ll 1/\omega_G\) Then the search probability is small but multiple repetitions of the algorithm allow to detect the searched state after a number of quantum operations \( N_{op} \sim t_{dec} n_g /w_G\) where the probability of searched state is \(w_G \sim t_{dec}^2/N\). The number of quantum operations for this strategy is \( N_{op} \sim (\varepsilon n_g)^2 N\)
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Received: 1st July 2004, Published online: 31 August 2004
PACS:
03.67.Lx Quantum Computation - 24.10.Cn Many-body theory - 73.43.Nq Quantum phase transitions
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Pomeransky, A.A., Zhirov, O.V. & Shepelyansky, D.L. Phase diagram for the Grover algorithm with static imperfections. Eur. Phys. J. D 31, 131–135 (2004). https://doi.org/10.1140/epjd/e2004-00113-4
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DOI: https://doi.org/10.1140/epjd/e2004-00113-4