We propose to store non-classical states of light into the macroscopic collective nuclear spin ($10^{18}$ atoms) of a $^3$He vapor, using metastability exchange collisions. These collisions, commonly used to transfer orientation from the metastable state $2^{3}S\_1$ to the ground state state of $^3$He, can also transfer quantum correlations. This gives a possible experimental scheme to map a squeezed vacuum field state onto a nuclear spin state with very long storage times (hours).
The coherent high-fidelity generation of nuclear spins in long-lived singlet states which may find application as quantum memory or sensor represents a considerable experimental challenge. Here we propose a dissipative scheme that achieves the preparation of pairs of nuclear spins in long-lived singlet states by a protocol that combines the interaction between the nuclei and a periodically reset electron spin of an NV center with local rf-control of the nuclear spins. The final state of this protocol is independent of the initial preparation of the nuclei, is robust to external field fluctuati…
We propose to create and stabilize long-lived macroscopic quantum superposition states in atomic ensembles. We show that using a fully quantum parametric amplifier can cause the simultaneous decay of two atoms and, in turn, create stabilized atomic Schrödinger cat states. Remarkably, even with modest parameters these intracavity atomic cat states can have an extremely long lifetime, up to \emph{4 orders of magnitude} longer than that of intracavity photonic cat states under the same parameter conditions, reaching \emph{tens of milliseconds}. This lifetime of atomic cat states is ultimately lim…
We have studied the role of thermalization in lifetime reduction of quantum memory based on multi-atomic ensembles. Herein, it is shown to be impossible to remove the thermaization-caused decoherence in such systems using the methods of dynamical decoupling. We have analyzed the existing models of the thermalization and have proposed a new understanding of the thermalization as a result of the internal processes which are not described in the unitary quantum dynamics formalism. The possible ways for reducing the negative influence of thermalization on the quantum memory lifetime are also discu…
We demonstrate experimentally a robust quantum memory using a magnetic-field-independent hyperfine transition in 9Be+ atomic ion qubits at a magnetic field B ~= 0.01194 T. We observe that the single physical qubit memory coherence time is greater than 10 seconds, an improvement of approximately five orders of magnitude from previous experiments with 9Be+. We also observe long coherence times of decoherence-free subspace logical qubits comprising two entangled physical qubits and discuss the merits of each type of qubit.
An ensemble of nuclear spin-pairs under certain conditions is known to exhibit singlet state life-times much longer than other non-equilibrium states. This property of singlet state can be exploited in quantum information processing for efficient initialization of quantum registers. Here we describe a general method of initialization and experimentally demonstrate it with two-, three-, and four-qubit nuclear spin registers.
We report an experiment on mapping a quantum state of light onto the ground state spin of an ensemble of Cs atoms with the life time of 2 milliseconds. Quantum memory for one of the two quadrature phase operators of light is demonstrated with vacuum and squeezed states of light. The sensitivity of the mapping procedure at the level of approximately one photon/sec per Hz is shown. The results pave the road towards complete (storing both quadrature phase observables) quantum memory for Gaussian states of light. The experiment also sheds new light on fundamental limits of sensitivity of the magne…
A solution with hyperpolarized nuclear spins encoded into a long-lived state has been utilized for sensing chemical phenomena. In a conventional way, nuclear spins are hyperpolarized at very low temperatures. In this work, we demonstrate the encoding of a four-nuclear-spin system hyperpolarized at room temperature into a long-lived state in a solution. We apply the solution with the long-lived state as a sensor in ligand--receptor binding experiments.
Nuclear spins of noble-gas atoms are exceptionally isolated from the environment and can maintain their quantum properties for hours at room temperature. Here we develop a mechanism for entangling two such distant macroscopic ensembles by using coherent light input. The interaction between the light and the noble-gas spins in each ensemble is mediated by spin-exchange collisions with alkali-metal spins, which are only virtually excited. The relevant conditions for experimental realizations with ^{3}\text{He} or ^{129}\text{Xe} are outlined.
A quantum repeater at telecommunications wavelengths with long-lived atomic memory is proposed, and its critical elements are experimentally demonstrated using a cold atomic ensemble. Via atomic cascade emission, an entangled pair of 1530 nm and 780 nm photons is generated. The former is ideal for long-distance quantum communication, and the latter is naturally suited for mapping to a long-lived atomic memory. Together with our previous demonstration of photonic-to-atomic qubit conversion, both of the essential elements for the proposed telecommunications quantum repeater have now been realize…
Algorithmic cooling methods manipulate an open quantum system in order to lower its temperature below that of the environment. We show that significant cooling is achieved on an ensemble of spin-pair systems by exploiting the long-lived nuclear singlet state, which is an antisymmetric quantum superposition of the "up" and "down" qubit states. The effect is demonstrated by nuclear magnetic resonance (NMR) experiments on a molecular system containing a coupled pair of near-equivalent 13C nuclei. The populations of the system are subjected to a repeating sequence of cyclic permutations separated …
153Eu3+:Y2SiO5 is a very attractive candidate for a long lived, multimode quantum memory due to the long spin coherence time (~15 ms), the relatively large hyperfine splitting (100 MHz) and the narrow optical homogeneous linewidth (~100 Hz). Here we show an atomic frequency comb memory with spin wave storage in a promising material 153Eu3+:Y2SiO5, reaching storage times slightly beyond 10 μs. We analyze the efficiency of the storage process and discuss ways of improving it. We also measure the inhomogeneous spin linewidth of 153Eu3+:Y2SiO5, which we find to be 69 \pm 3 kHz. These results repre…
We report experimental observations of the long-lived rhodium Mossbauer emissions by the time- and energy-resolved spectroscopy. The extraordinary observations manifest the open-up of photonic band gap in analogy to the superconducting gap of remarkable symmetry breakings at transition point. These observations are of potential importance for detecting gravitational waves and development of the two-photon gamma laser. Firstly, phase transitions shown by spectral evolution of characteristic emissions reveal the different aggregate exciton orderings at room temperature. Six different phases are …
We demonstrate that dynamical probes provide direct means of detecting the topological phase transition (TPT) between conventional and topological phases, which would otherwise be difficult to access because of loss or heating processes. We propose to avoid such heating by rapidly quenching in and out of the short-lived topological phase across the transition that supports gapless excitations. Following the quench, the distribution of excitations in the final conventional phase carries signatures of the TPT. We apply this strategy to study the TPT into a Majorana-carrying topological phase pre…
We study how to efficiently manipulate and store quantum information between optical fields and atomic ensembles. We show how various non-dissipative transfer schemes can be used to transfer and store quantum states such as squeezed vacuum states or entangled states into the long-lived ground state spins of atomic ensembles.
We propose to entangle macroscopic atomic ensembles in cavity using EPR-correlated beams. We show how the field entanglement can be almost perfectly mapped onto the long-lived atomic spins associated with the ground states of the ensembles, and how it can be retrieved in the fields exiting the cavities after a variable storage time. Such a continuous variable quantum memory is of interest for manipulating entanglement in quantum networks.
Long-lived population storage in optically pumped levels of rare-earth ions doped into solids, referred to as persistent spectral hole burning, is of significant fundamental and technological interest. However, the demonstration of deep and persistent holes in rare-earth ion doped amorphous hosts, e.g. glasses, has remained an open challenge since many decades -- a fact that motivates our work towards a better understanding of the interaction between impurities and vibrational modes in glasses. Here we report the first observation and detailed characterization of such holes in an erbium-doped …
Using a quantum theory for an ensemble of three-level atoms (lambda) placed in an optical cavity abd driven by electromagnetic fields, we show that the long-lived spin associated with the ground state sublevels can be squeezed. Two kinds of squeezing are obtained: self-spin squeezing, when the input fields are coherent states and the atomic ensemble exhibit a large non-linearity; squeezing transfer, when one of the incoming fields is squeezed.
We report an observation of extremely long-lived spin states in systems of dipolar-coupled nuclear spins in solids. The 'suspended echo' experiment uses a simple stimulated echo pulse sequence and creates non-equilibrium states which live many orders of magnitude longer than the characteristic time of spin-spin dynamics T2. Large amounts of information can be encoded in such long-lived states, stored in a form of multi-spin correlations, and subsequently retrieved by an application of a single 'reading' pulse.
To establish an applicable system for advanced quantum information processing between light and atoms, we have demonstrated the quantum non-demolition (QND) measurement with a collective spin of cold ytterbium atoms (171Yb), and observed 1.8 (-1.5, +2.4) dB spin squeezing. Since a 171Yb atom has only a nuclear spin of 1/2 in the ground state, the system is the simplest spin ensemble and robust against decoherence. We used very short pulses with the width of 100 ns, so the interaction time became much shorter than the decoherence time, which is important for multi-step quantum information proce…
A method for generating a mesoscopic superposition state of the collective spin variable of a gas of atoms is proposed. The state consists of a superposition of the atomic spins pointing in two slightly different directions. It is obtained by using off resonant light to carry out Quantum Non Demolition Measurements of the spins. The relevant experimental conditions, which require very dense atomic samples, can be realized with presently available techniques. Long-lived atomic superposition states may become useful as an off-line resource for quantum computing with otherwise linear operations.
Coupled pairs of spin-1/2 nuclei support one singlet state and three triplet states. In many circumstances the nuclear singlet order, defined as the difference between the singlet population and the mean of the triplet populations, is a long-lived state which persists for a relatively long time in solution. Various methods have been proposed for generating singlet order, starting from nuclear magnetization. This requires the stimulation of singlet-to-triplet transitions by modulated radiofrequency fields. We show that a recently described pulse sequence, known as PulsePol (Schwartz $\textit{et…
Understanding fully the dynamics of coupled electron-nuclear spin systems, which are important for the development of long-lived qubits based on solid-state systems, remains a challenge. We show that in a singly charged semiconductor quantum dot with inhomogeneous hyperfine coupling, the nuclear spins relatively strongly coupled to the electron spin form a polarized core during the dynamical polarization process. The polarized core provides a protection effect against the electron spin relaxation, reducing the decay rate by a factor of $N_1$, the number of the nuclear spins in the polarized co…
Nanoscale systems offer key capabilities for quantum technologies that include single qubit control and readout, multiple qubit gate operation, extremely sensitive and localized sensing and imaging, as well as the ability to build hybrid quantum systems. To fully exploit these functionalities, multiple degrees of freedom are highly desirable: in this respect, nanoscale systems that coherently couple to light and possess spins, allow for storage of photonic qubits or light-matter entanglement together with processing capabilities. In addition, all-optical control of spins can be possible for fa…
Photon loss in optical fibers prevents long-distance distribution of quantum information on the ground. Quantum repeater is proposed to overcome this problem, but the communication distance is still limited so far because of the system complexity of the quantum repeater scheme. Alternative solutions include transportable quantum memory and quantum-memory-equipped satellites, where long-lived optical quantum memories are the key components to realize global quantum communication. However, the longest storage time of the optical memories demonstrated so far is approximately 1 minute. Here, by em…
We measure the lifetime of long-lived nuclear spin singlet states as a function of the strength of the RF spin-locking field and present a simple theoretical model that agrees well with our measurements, including the low-RF-power regime. We also measure the lifetime of a long-lived coherence between singlet and triplet states that does not require a spin-locking field for preservation. Our results indicate that for many molecules, singlet states can be created using weak RF spin-locking fields: more than two orders of magnitude lower RF power than in previous studies. Our findings suggest tha…
We probe small scalar coupling differences via the coherent interactions between two nuclear spin singlet states in organic molecules. We show that the spin-lock induced crossing (SLIC) technique enables the coherent transfer of singlet order between one spin pair and another. The transfer is mediated by the difference in cis and trans vicinal J couplings among the spins. By measuring the transfer rate, we calculate a J coupling difference of $8 \pm 2$ mHz in phenylalanine-glycine-glycine and $2.57 \pm 0.04$ Hz in glutamate. We also characterize a coherence between two singlet states in glutam…
Solids and rigid tissues such as bone, ligaments, and tendons, typically appear dark in magnetic resonance imaging (MRI), which is due to the extremely short-lived proton nuclear magnetic resonance (NMR) signals. This short lifetime is due to strong dipolar interactions between immobilized proton spins, which render it challenging to detect these signals with sufficient resolution and sensitivity. Here we show the possibility of exciting long-lived signals in cortical bone tissue with a signature consistent with that of bound water signals. Contrary to long-standing belief, it is further shown…
According to the Schiff theorem nuclear electric dipole moment (EDM) is completely shielded in a neutral atom by electrons. This makes a static nuclear electric dipole moment (EDM) unobservable. Interaction with the axion dark matter field generates nuclear EDM $d=d_0 \cos (ωt)$ oscillating with the frequency $ω= m_a c^2/\hbar$ . This EDM generates atomic EDM proportional to $ω^2$. This effect is strongly enhanced in molecules since nuclei move slowly and do not produce as efficient screening of oscillating nuclear EDM as electrons do. An additional strong enhancement comes due to a small ener…
Dipole-dipole interactions are at the origin of long-lived collective atomic states, often called subradiant, which are explored for their potential use in novel photonic devices or in quantum protocols. Here, we study subradiance beyond linear optics and experimentally demonstrate a two hundred-fold increase in the population of these modes, as the saturation parameter of the driving field is increased. We attribute this enhancement to a mechanism similar to optical pumping through the well-coupled superradiant states. The lifetimes are unaffected by the pump strength, as the system is ultima…
Approximate probabilities of formation of various atoms and ions in different bound states are determined for the exothermic nuclear $(n,{}^{6}$Li$;t,{}^{4}$He)-reaction of atomic lithium-6 with slow neutrons. In our calculations of the final state probabilities we have assumed that the incident lithium atom is in its ground (doublet) atomic ${}^2S(L = 0)-$state. It is straightforward to generalize our analysis to other bound states of the three-electron Li atom.
Nuclear spin imaging at the atomic level is essential for the understanding of fundamental biological phenomena and for applications such as drug discovery. The advent of novel nano-scale sensors has given hope of achieving the long-standing goal of single-protein, high spatial-resolution structure determination in their natural environment and ambient conditions. In particular, quantum sensors based on the spin-dependent photoluminescence of Nitrogen Vacancy (NV) centers in diamond have recently been used to detect nanoscale ensembles of external nuclear spins. While NV sensitivity is approac…
Single-molecule nuclear magnetic resonance (NMR) is a crown-jewel challenge in the field of magnetic resonance spectroscopy and has important applications in chemical analysis and in quantum computing. Recently, it becomes possible to tackle this grand challenge thanks to experimental advances in preserving quantum coherence of nitrogen-vacancy (NV) center spins in diamond as a sensitive probe and theoretical proposals on atomic-scale magnetometry via dynamical decoupling control. Through decoherence measurement of NV centers under dynamical decoupling control, sensing of single $^{13}\textbf{…
Nuclear spins support long lived quantum coherence due to weak coupling to the environment, but are difficult to rapidly control using nuclear magnetic resonance (NMR) as a result of the small nuclear magnetic moment. We demonstrate a fast ~ 500 ns nuclear spin phase gate on a 14N nuclear spin qubit intrinsic to a nitrogen-vacancy (NV) center in diamond. The phase gate is enabled by the hyperfine interaction and off-resonance driving of electron spin transitions. Repeated applications of the phase gate bang-bang decouple the nuclear spin from the environment, locking the spin state for up to ~…
A state-of-the-art approach for calculating the finite nuclear size correction to atomic energy levels and the bound-electron $g$ factor is introduced and demonstrated for a series of highly charged hydrogen-like ions. Firstly, self-consistent mean-field calculations based on the Skyrme-type nuclear interaction are employed in order to produce a realistic nuclear proton distribution. In the second step, the obtained nuclear charge density is used to construct the potential of an extended nucleus, and the Dirac equation is solved numerically. The ambiguity in the choice of a Skyrme parametrizat…
Optical atomic clocks using highly-charged ions hold an intriguing promise of metrology at the 19th significant figure. Here we study transitions within the $4f^{12}$ ground-state electronic configuration of highly charged ions. We consider isotopes lacking hyperfine structure and show that the detrimental effects of coupling of electronic quadrupole moments to gradients of trapping electric field can be effectively reduced by using specially chosen virtual clock transitions. The estimated systematic fractional clock accuracy is shown to be below $10^{-19}$.
Many-body eigenfunctions of the total spin operator can be constructed from the spin and spatial wavefunctions with non-trivial permutation symmetries. Spin-dependent interactions can lead to relaxation of the spin eigenstates to the thermal equilibrium. A mechanism that stabilizes the many-body entangled states is proposed here. Surprisingly, in spite coupling with the chaotic motion of the spatial degrees of freedom, the spin relaxation can be suppressed by destructive quantum interference due to spherical vector and tensor terms of the spin-dependent interactions. Tuning the scattering leng…
This paper addresses the three following questions. (i) How the structures of group and of chain of groups enter nuclear, atomic and molecular spectroscopy? (ii) How these structures can be exploited, in a quantum- mechanical framework, in the problems of state labelling and (external) symmetry breaking? (iii) How it is possible to associate a Wigner-Racah algebra to a group or a chain of groups for making easier the calculation of quantum-mechanical matrix elements? Numerous examples illustrate the philosophy of qualitative and quantitative applications to spectroscopy.
Linear arrays of trapped and laser cooled atomic ions are a versatile platform for studying emergent phenomena in strongly-interacting many-body systems. Effective spins are encoded in long-lived electronic levels of each ion and made to interact through laser mediated optical dipole forces. The advantages of experiments with cold trapped ions, including high spatiotemporal resolution, decoupling from the external environment, and control over the system Hamiltonian, are used to measure quantum effects not always accessible in natural condensed matter samples. In this review we highlight recen…
