Dilute Measurement-Induced Cooling into Many-Body Ground States (original) (raw)

Ground-state cooling of quantum systems via a one-shot measurement

We prove that there exists a family of quantum systems that can be cooled to their ground states by a one-shot projective measurement on the ancillas coupled to these systems. Consequently, this proof gives rise to the conditions for achieving the one-shot measurement ground-state cooling (OSMGSC). We also propose a general procedure for finding unitary propagators and corresponding Hamiltonians to realize such cooling by means of inverse engineering techniques.

Measuring the temperature of cold many-body quantum systems

Physical Review B, 2018

Precise low-temperature thermometry is a key requirement for virtually any quantum technological application. Unfortunately, as the temperature T decreases, the errors in its estimation diverge very quickly. In this paper, we determine exactly how quickly this may be. We rigorously prove that the "conventional wisdom" of low-T thermometry being exponentially inefficient, is limited to local thermometry on translationally invariant systems with short-range interactions, featuring a non-zero gap above the ground state. This result applies very generally to spin and harmonic lattices. On the other hand, we show that a power-law-like scaling is the hallmark of local thermometry on gapless systems. Focusing on thermometry on one node of a harmonic lattice, we obtain valuable physical insight into the switching between the two types of scaling. In particular, we map the problem to an equivalent setup, consisting of a Brownian thermometer coupled to an equilibrium reservoir. This mapping allows us to prove that, surprisingly, the relative error of local thermometry on gapless harmonic lattices does not diverge as T → 0; rather, it saturates to a constant. As a useful by-product, we prove that the low-T sensitivity of a harmonic probe arbitrarily strongly coupled to a bosonic reservoir by means of a generic Ohmic interaction, always scales as T 2 for T → 0. Our results thus identify the energy gap between the ground and first excited states of the global system as the key parameter in local thermometry, and ultimately provide clues to devising practical thermometric strategies deep in the ultra-cold regime.

Measurement induced dynamics for quantum communication in strongly correlated systems

Physical Review A

We show that a single qubit measurement followed by a unitary operation which is determined by the random outcome of the measurement can be used for both encoding the information and performing a quantum quench in a strongly correlated anti-ferromagnetic many-body system. The proposed mechanism, does not need any local control over the interaction of the system and instead exploits local operations on the quantum state of the system and harnesses the inherent entanglement in the ground state of the strongly correlated system. The performance remains always better than the classical threshold for chains up to length 50. Cold atoms in optical lattices are ideal physical setup for realizing our proposal and all the ingredients needed for local measurements and unitary operations are already available in the experiments.

Probing the temperature of cold many-body quantum systems

2017

It is "conventional wisdom" that the uncertainty of local temperature measurements on equilibrium systems diverges exponentially fast as their temperature T drops to zero. In contrast, some exactly solvable models showcase a more benign power-law-like scaling, when only a small non-equilibrium fragment of the equilibrium system is measured. Does this mean that a part may contain more information about the global temperature than the whole? Certainly not. Here, we resolve this apparent paradox. First, we prove that local quantum thermometry at low T is exponentially inefficient in non-critical, gapped, and infinite spin and harmonic lattices. In contrast, we show through an open-system analysis, that the thermal sensitivity of a harmonic thermometer (probe) jointly equilibrated with a reservoir (sample) by means of an Ohmic coupling scheme, displays a distinctive power-law-like behavior as T → 0. To reconcile these two results, we exploit the fact that local thermometry on ...

Measurement Quench in Many-Body Systems

Physical review letters, 2018

Measurement is one of the key concepts which discriminates classical and quantum physics. Unlike classical systems, a measurement on a quantum system typically alters it drastically as a result of wave function collapse. Here we suggest that this feature can be exploited for inducing quench dynamics in a many-body system while leaving its Hamiltonian unchanged. Importantly, by doing away with dedicated macroscopic devices for inducing a quench-using instead the indispensable measurement apparatus only-the protocol is expected to be easier to implement and more resilient against decoherence. By way of various case studies, we show that our scheme also has decisive advantages beyond reducing decoherence-for spectroscopy purposes and probing nonequilibrium scaling of critical and quantum impurity many-body systems.

Measurement enhances long-distance entanglement generation in spin chains with dissipative processes

The European Physical Journal D, 2018

In this paper, effects of the regular measurements on a noisy channel has been investigated. The strategy introduced by A. Bayat, and Y. Omar [New J. Phys. 17, 103041 (2015)] is followed to suppress dephasing and dissipation effects in a noisy spin channel and generate long distance entanglement by global measurement on the channel. A regular global measurements performed on spin channel weakly coupled to the sender and receiver qubits via XX interaction. This scheme is applied for the dephasing and dissipation in non-zero temperature processes separately and the results show that amounts of achieved entanglement enhanced rather than the no-measurement approach.

Measurement-induced, spatially-extended entanglement in a hot, strongly-interacting atomic system

Nature Communications

Quantum technologies use entanglement to outperform classical technologies, and often employ strong cooling and isolation to protect entangled entities from decoherence by random interactions. Here we show that the opposite strategy—promoting random interactions—can help generate and preserve entanglement. We use optical quantum non-demolition measurement to produce entanglement in a hot alkali vapor, in a regime dominated by random spin-exchange collisions. We use Bayesian statistics and spin-squeezing inequalities to show that at least 1.52(4) × 1013 of the 5.32(12) × 1013 participating atoms enter into singlet-type entangled states, which persist for tens of spin-thermalization times and span thousands of times the nearest-neighbor distance. The results show that high temperatures and strong random interactions need not destroy many-body quantum coherence, that collective measurement can produce very complex entangled states, and that the hot, strongly-interacting media now in us...

Thermal effects on quantum communication through spin chains

Physical Review A, 2005

We study the effect of thermal fluctuations in a recently proposed protocol for transmission of unknown quantum states through quantum spin chains. We develop a low temperature expansion for general spin chains. We then apply this formalism to study exactly thermal effects on short spin chains of four spins. We show that optimal times for extraction of output states are almost independent of the temperature which lowers only the fidelity of the channel. Moreover we show that thermal effects are smaller in the anti-ferromagnetic chains than the ferromagnetic ones.

Experimental Verification of Many-Body Entanglement Using Thermodynamic Quantities

arXiv (Cornell University), 2023

The phenomenon of quantum entanglement underlies several important protocols that enable emerging quantum technologies. Being an extremely delicate resource entangled states easily get perturbed by their external environment, and thus makes the question of entanglement certification immensely crucial for successful implementation of the protocols involving entanglement. In this work, we propose a set of entanglement criteria for multi-qubit systems that can be easily verified by measuring certain thermodynamic quantities. In particular, the criteria depend on the difference in optimal works extractable from an isolated quantum system under global and local interactions, respectively. As a proof of principle, we demonstrate the proposed thermodynamic criteria on nuclear spin registers of up to 10 qubits using Nuclear Magnetic Resonance architecture. We prepare noisy Greenberger-Horne-Zeilinger class of states in star-topology systems and certify their entanglement through our proposed criteria. We also provide elegant means of entanglement certification in many-body systems when only partial or even no knowledge about the state is available.

Cooling atoms into entangled states

2009

We discuss the possibility of preparing highly entangled states by simply cooling atoms into the ground state of an applied interaction Hamiltonian. As in laser sideband cooling, we take advantage of a relatively large detuning of the desired state, while all other qubit states experience resonant laser driving. Once spontaneous emission from excited atomic states prepares the system in its ground state, it remains there with a very high fidelity for a wide range of experimental parameters and all possible initial states. After presenting the general theory, we discuss concrete applications with one and two qubits.