ms_phases_multitone

Graph.ms_phases_multitone(drives, lamb_dicke_parameters, relative_detunings, sample_times=None, *, name=None)

Calculate the relative phases for all pairs of ions described by a Mølmer–Sørensen-type interaction where the ions are being addressed by a multitone global beam.

Use this function to calculate the acquired phases for all ion pairs at the final time of the drives, or at the sample times that you provide.

Parameters
  • drives (list[Pwc(1D, complex)]) – A list of piecewise-constant drives \(\{\gamma_\xi\}\) for each of the tones of the global beam. The number of drives must be the same as the number of tones of the global beam, \(M\). Drive values must be one-dimensional arrays and in rad/s. Drive durations must be in seconds. All drives must have the same total duration, but can have different numbers of segments.

  • lamb_dicke_parameters (np.ndarray) – A 4D array of parameters \(\{\eta_{\xi jkl}\}\) specifying the laser-ion coupling strength. Its shape must be (M, 3, N, N) where the first dimension \(\xi\) indicates the tone of the global beam, the second dimension \(j\) indicates the axis, the third dimension \(k\) indicates the collective mode number, and the fourth dimension \(l\) indicates the ion.

  • relative_detunings (np.ndarray) – A 3D array \(\{\delta_{\xi jk} = \nu_{jk} - \delta_\xi \}\) specifying the difference (in Hz) between each motional mode frequency \(\nu_{jk}\) and the laser detunings for each tone, \(\delta_\xi\) (the detuning from the qubit transition frequency \(\omega_0\)). Its shape must be (M, 3, N) where the first dimension \(\xi\) indicates the tone of the global beam, the second dimension \(j\) indicates the axis and the third dimension \(k\) indicates the collective mode number.

  • sample_times (np.ndarray, optional) – A 1D array of length \(T\) specifying the times \(\{t_i\}\) (in seconds) at which this function calculates the relative phases. If you omit it, this function calculates the phases only at the final time of the drives. If provided, it must be ordered and contain at least one element.

  • name (str, optional) – The name of the node.

Returns

Acquired phases \(\{\phi_{jk}(t_i) + \phi_{kj}(t_i)\}\) for all ion pairs. If you provide sample_times, the shape of the returned value is (T, N, N), where the first dimension indicates the time; the second and the third dimensions indicate the ion. Otherwise, the shape is (N, N) where both dimensions indicate the ion. The relative phases are stored as a strictly lower triangular matrix. See the notes part for details.

Return type

Tensor(real)

See also

calculate_ion_chain_properties()

Function to calculate the properties of an ion chain.

ms_infidelity()

Final operational infidelity of a Mølmer–Sørensen gate.

ms_phases()

Corresponding operation for single-tone individually-addressed beams.

Notes

The interaction Hamiltonian for Mølmer–Sørensen-type operations in the rotating frame for a multitone global beam is:

\[H_I(t) = i\hbar\sum_{j = 1}^N \sigma_{x, j} \sum_{p = 1}^{3N} \sum_{\xi = 1}^M (-\beta_{\xi pj}^*(t)a_p + \beta_{\xi pj}(t) a_p^\dagger) ,\]

where \(\sigma_{x, j}\) is the Pauli \(X\) operator for the ion \(j\) and \(\beta_{\xi pj}(t) = \eta_{\xi pj} \frac{\gamma_\xi(t)}{2} e^{i\delta_{\xi p} t}\), indicating the coupling of the ion \(j\) to the motional mode \(p\). The corresponding unitary operation is given by:

\[U(t) = \exp\left[ \sum_{j=1}^N \sigma_{x, j} B_j(t) + i\sum_{j=1}^N \sum_{k=1}^{j - 1} (\phi_{jk}(t) + \phi_{kj}(t)) \sigma_{x, j} \sigma_{x, k} \right] ,\]

where

\[ \begin{align}\begin{aligned}B_j(t) &\equiv \sum_{p = 1}^{3N} \sum_{\xi = 1}^M \left(\eta_{\xi pj}\alpha_{\xi pj}(t)a_p^\dagger - \eta_{\xi pj}^{\ast}\alpha_{\xi pj}^\ast(t)a_p \right) ,\\\phi_{jk}(t) &\equiv \mathrm{Im} \left[ \sum_{p=1}^{3N} \sum_{\xi_1 = 1}^M \sum_{\xi_2 = 1}^M \int_{0}^{t} d \tau_1 \int_{0}^{\tau_1} d \tau_2 \beta_{\xi_1 pj}(\tau_1)\beta_{\xi_2 pk}^{\ast}(\tau_2) \right] ,\end{aligned}\end{align} \]

with \(\alpha_{\xi pj}(t) = \int_0^t d\tau \frac{\gamma_\xi(\tau)}{2} e^{i \delta_{\xi p} \tau}\).

This function calculates the relative phases \(\phi_{jk}(t_i) + \phi_{kj}(t_i)\) for all ions pairs at time \(t_i\) and stores the result in the form of a strictly lower triangular matrix. That is, the \(jk\)-th element of that matrix records the relative phase between the ion \(j\) and \(k\), while the elements with indices \(j \leq k\) are zeros.