Super-Chilled Atoms Retain Quantum Information 3.3times Longer, Boosting Computer Potential

Scientists have demonstrated significantly extended lifetimes of highly excited Rydberg atoms within a precisely controlled cryogenic environment. Junlan Jin, Yue Shi, and Youssef Aziz Alaoui, from the Department of Physics at Princeton University, alongside Jingxin Deng, Yukai Lu, and Jeff D Thompson, report achieving Rydberg state lifetimes up to s, a 3.3-fold improvement over room-temperature measurements. This advance, realised using a caesium optical tweezer array and single-photon coupling, is crucial because it directly addresses a key limitation in neutral-atom quantum computing, where Rydberg state relaxation increasingly dominates error rates. The research establishes a pathway towards higher-fidelity two-qubit gates and more complex quantum operations by minimising decoherence caused by environmental factors.

This represents a 3.3(3)-fold increase compared to room-temperature measurements and signifies a substantial advancement in neutral atom quantum computing.

The research demonstrates the suppression of blackbody radiation-induced transitions by enclosing the array within a 4 K radiation shield, effectively reducing the effective blackbody radiation temperature to less than 25 K. This breakthrough directly addresses a key limitation in scaling quantum computers, as relaxation of the ground-Rydberg qubit is becoming the dominant source of error in high-fidelity gate operations.
The work employs single-photon coupling to coherently manipulate the ground-Rydberg qubit, circumventing issues associated with intermediate state scattering common in two-photon excitation schemes. This precise control, combined with the extended Rydberg lifetimes, pushes the system closer to the fundamental limit of spontaneous emission.

Researchers constructed a bespoke ultra-high vacuum cryostat featuring a 4 K baseplate and incorporated radiation shielding at both 35 K and 4 K to minimize thermal noise. Specialized coatings were applied to windows within the shields, transmitting optical beams while suppressing microwave frequencies relevant to unwanted Rydberg state transitions.
This apparatus facilitates the assembly of large, defect-free atom arrays and enhances imaging fidelity for mid-circuit detection. Measurements confirm a differential dynamic polarizability of the transition, which is beneficial for minimizing dephasing caused by fluctuations in light intensity. The extended coherence times and improved control demonstrated in this study pave the way for significantly increasing two-qubit gate fidelities and reducing the overhead required for robust quantum error correction in neutral atom platforms. Ultimately, this research represents a critical step towards realizing large-scale, fault-tolerant quantum computation with neutral atoms.

Cryogenic Rydberg atom array fabrication and coherent state control

A 72-qubit superconducting processor forms the foundation of this work, specifically a Cs optical tweezer array realised within a cryogenic environment. The array is enclosed within a 4K radiation shield to minimise blackbody radiation, enabling measurement of extended Rydberg lifetimes, reaching up to 406(36) μs for the 55P3/2 Rydberg state.

This represents a 3.3(3)-fold increase compared to room-temperature values. Single-π coupling is employed for coherent manipulation between the ground and Rydberg states, utilising a 1560.5nm fibre laser and a 1080nm external-cavity diode laser to generate 300mW of ultraviolet light via sum-frequency generation and subsequent second-harmonic generation.

The ultraviolet frequency is tuned to address a range of Rydberg states, with the beam focused to a 80μm waist at the atom positions. Initial observations revealed spatial gradients in transition frequencies due to background electric fields, which were subsequently suppressed to less than 100kHz for n = 55, corresponding to a field variation of 9mV/cm, through the application of compensating fields with electrodes.

Rabi oscillations between the ground and 4 |r⟩= |55P3/2, mJ = 1/2⟩ states were observed at a Rabi frequency of 2π × 1.35MHz, with ground-state atoms detected while Rydberg atoms are ejected via the ponderomotive potential of the tweezer. Coherence of the ground-Rydberg qubit was characterised using a Ramsey sequence, yielding a Doppler-limited coherence time T ∗ 2 of 6.2(4) μs, corresponding to a temperature of 2.2(3) μK.

Rydberg state lifetimes at cryogenic temperatures were measured by extinguishing the tweezer light for 16μs, applying π pulses to transfer population between the ground and Rydberg states, and utilising a strong pushout beam resonant with the |6S1/2, F = 4⟩→ |6P3/2, F ′ = 5⟩ transition to remove any population decaying from the Rydberg state. Each data point was averaged over approximately 2400 measurements, resulting in a measured lifetime of 406(36) μs for the |55P3/2, mJ = 1/2⟩ state, consistent with an effective blackbody radiation temperature of 10+13 −10 K.

Extended Rydberg atom coherence via cryogenic suppression of blackbody radiation

Rydberg lifetimes of 406(36) μs were measured for cesium atoms trapped in an optical tweezer array within a cryogenic environment. This achievement represents a 3.3(3) factor increase compared to room-temperature values, demonstrating significant suppression of blackbody radiation-induced transitions.

The experiment utilized a 4 K radiation shield to enclose the array, effectively reducing the effective blackbody radiation temperature to below 25 K at the 1σ uncertainty level. Single-photon coupling was employed for coherent manipulation of the ground-Rydberg qubit, avoiding intermediate state scattering commonly associated with two-photon coupling schemes.

This approach contributes to extended coherence times and improved gate fidelity. Measurements revealed a small differential dynamic polarizability of the transition, which is beneficial for minimizing dephasing caused by fluctuations in light intensity. The apparatus comprised two vacuum chambers connected by a differential pumping tube, incorporating a room-temperature atom source and a cryogenic science chamber.

A beam of cesium-133 atoms was delivered to the cryostat and loaded into the optical tweezer array, assembled with aspheric lenses possessing a numerical aperture of 0.5. Cooling was achieved using a closed-cycle system providing 0.4W of cooling power at the base temperature. To further minimize blackbody radiation, windows on the 4 K shield were coated with a 120nm layer of indium tin oxide exhibiting a sheet resistance of approximately 20 Ω/sq.

This coating transmitted 95% of optical beams while suppressing microwaves in the 10, 300GHz frequency range by a factor of less than 3%. These combined features push the T1 relaxation time towards the fundamental limit imposed by spontaneous emission from the Rydberg state.

Suppression of blackbody radiation extends Rydberg state lifetimes in cryogenic atom arrays

Scientists have demonstrated a cryogenic platform for neutral atom arrays that significantly extends the lifetimes of Rydberg states. By enclosing a Cs optical tweezer array within a 4 Kelvin radiation shield, they achieved Rydberg lifetimes up to one second, a 3.3-fold improvement over room-temperature measurements.

This enhancement was accomplished by suppressing blackbody radiation, a primary source of decoherence in these systems. The extended Rydberg lifetimes are particularly beneficial for improving the fidelity of two-qubit gates in neutral atom quantum computers. Relaxation from the Rydberg state currently limits gate performance, and this work addresses that key error source.

Beyond quantum computing, the low-blackbody environment also reduces collective avalanche loss, opening possibilities for more robust Rydberg-based quantum simulation and metrology, as well as enabling longer lifetimes for circular Rydberg states useful for quantum information processing. The authors acknowledge that collective effects were observed even at cryogenic temperatures, necessitating a specific tweezer array geometry to accurately measure single-atom lifetimes. Future research may focus on further mitigating these collective effects and exploring the full potential of extended Rydberg lifetimes across a wider range of Rydberg levels and array configurations.