Ultracold polar molecules as qudits

Abstract

We discuss how the internal structure of ultracold molecules, trapped in the motional ground state of optical tweezers, can be used to implement qudits. We explore the rotational, fine and hyperfine structure of 40 Ca 19 F and 87 Rb 133 Cs, which are examples of molecules with 2 Σ and 1 Σ electronic ground states, respectively. In each case we identify a subset of levels within a single rotational manifold suitable to implement a four-level qudit. Quantum gates can be implemented using two-photon microwave transitions via levels in a neighboring rotational manifold. We discuss limitations to the usefulness of molecular qudits, arising from off-resonant excitation and decoherence. As an example, we present a protocol for using a molecular qudit of dimension d=4 to perform the Deutsch algorithm.

Robust entangling gate for polar molecules using magnetic and microwave fields

“…However, our scheme is not susceptible to decoherence and losses in the strongly interacting states because our large-EDM states are low-lying rotational states with negligible spontaneous decay rates ( 10 −8 s −1 [40]). This highlights one of the advantages of cold polar molecules for quantum information processing [25,26,31,40].…”

“…The field of ultracold molecules has seen enormous progress in the past few years, with landmark achievements such as the production of the first quantum-degenerate molecular Fermi gas [1], low-entropy molecular samples in optical lattices [2,3], trapping of single molecules in optical tweezers [4][5][6], and magneto-optical trapping and sub-Doppler cooling of molecules [7][8][9][10][11]. These results bring significantly closer a broad range of applications of ultracold molecules, from state-controlled chemistry [12][13][14][15][16][17] and novel tests of fundamental laws of nature [18][19][20][21] to new architectures for quantum computation [22][23][24][25][26], quantum simulation [27][28][29][30][31][32], and quantum sensing [33,34].…”

Prospects of Forming High-Spin Polar Molecules from Ultracold Atoms

“…It should be straightforward to transfer population between these states and create coherent superpositions of them with microwave pulses, as has been achieved for alkali-metal dimers [101]. The large number of states available offer the opportunity to create fully controllable high-dimensional quantum systems, which may be used as qudits for quantum computation [18]. In zero electric field, states with positive and negative values of Ω combine to form pairs of states of opposite parity.…”

“…Tunable Feshbach resonances also form the basis of magnetoassociation [4] and are crucial in the formation of ultracold ground-state molecules composed of alkalimetal atoms [5][6][7][8][9][10]. These molecules are now opening up new areas of research into dipolar physics [11][12][13][14], quantum simulation and computation [15][16][17][18], and controlled chemistry [19][20][21].…”

Encoding a qubit in a molecule

“…The rigid rotor Hamiltonian describing molecular rotational motion is inherently anharmonic; because the energy levels are unevenly spaced, transitions between levels can be individually addressed using microwave fields. Hence, proposals for storing quantum information in molecules [12][13][14][15][16][17][18][19][20][21][22][23] (see also [24,25]) typically pick out two low-lying long-lived energy eigenstates as basis states for a qubit. One can also introduce an external electric field, and encode a qubit using the resulting "pendular" eigenstates [26][27][28].…”