Pub Date : 2024-08-02DOI: 10.1038/s41567-024-02564-3
Yu-Te Hsu, Andreas Rydh, Maarten Berben, Caitlin Duffy, Alberto de la Torre, Robin S. Perry, Nigel E. Hussey
High-temperature superconductivity in cuprates emerges upon doping the parent Mott insulator. Key features of the low-doped cuprate superconductors include an effective carrier density that tracks the number of doped holes, the emergence of an anisotropic pseudogap that is characterized by disconnected Fermi arcs and the closure of the gap at a critical doping level. In Sr2IrO4, a spin–orbit-coupled Mott insulator often regarded as a 5d analogue of the cuprates, surface probes have also revealed the emergence of an anisotropic pseudogap and Fermi arcs under electron doping. However, neither the corresponding critical doping nor the bulk signatures of pseudogap closure have yet been observed. Here we demonstrate that electron-doped Sr2IrO4 exhibits a critical doping level with a marked crossover in the effective carrier density at low temperatures. This is accompanied by a five-orders-of-magnitude increase in conductivity and a sixfold enhancement in the electronic specific heat. These collective findings resemble the bulk pseudogap phenomenology in cuprates. However, given that electron-doped Sr2IrO4 is non-superconducting, it suggests that the pseudogap may not be a state of precursor pairing. Therefore, our results narrow the search for the key ingredient underpinning the formation of the superconducting condensate in doped Mott insulators. The pseudogap in cuprates is often linked to superconductivity. Now bulk evidence for a pseudogap is found in doped non-superconducting Sr2IrO4, revealing that pseudogaps in doped Mott insulators are not necessarily a precursor to superconductivity.
{"title":"Carrier density crossover and quasiparticle mass enhancement in a doped 5d Mott insulator","authors":"Yu-Te Hsu, Andreas Rydh, Maarten Berben, Caitlin Duffy, Alberto de la Torre, Robin S. Perry, Nigel E. Hussey","doi":"10.1038/s41567-024-02564-3","DOIUrl":"10.1038/s41567-024-02564-3","url":null,"abstract":"High-temperature superconductivity in cuprates emerges upon doping the parent Mott insulator. Key features of the low-doped cuprate superconductors include an effective carrier density that tracks the number of doped holes, the emergence of an anisotropic pseudogap that is characterized by disconnected Fermi arcs and the closure of the gap at a critical doping level. In Sr2IrO4, a spin–orbit-coupled Mott insulator often regarded as a 5d analogue of the cuprates, surface probes have also revealed the emergence of an anisotropic pseudogap and Fermi arcs under electron doping. However, neither the corresponding critical doping nor the bulk signatures of pseudogap closure have yet been observed. Here we demonstrate that electron-doped Sr2IrO4 exhibits a critical doping level with a marked crossover in the effective carrier density at low temperatures. This is accompanied by a five-orders-of-magnitude increase in conductivity and a sixfold enhancement in the electronic specific heat. These collective findings resemble the bulk pseudogap phenomenology in cuprates. However, given that electron-doped Sr2IrO4 is non-superconducting, it suggests that the pseudogap may not be a state of precursor pairing. Therefore, our results narrow the search for the key ingredient underpinning the formation of the superconducting condensate in doped Mott insulators. The pseudogap in cuprates is often linked to superconductivity. Now bulk evidence for a pseudogap is found in doped non-superconducting Sr2IrO4, revealing that pseudogaps in doped Mott insulators are not necessarily a precursor to superconductivity.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 10","pages":"1596-1602"},"PeriodicalIF":17.6,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141877404","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-02DOI: 10.1038/s41567-024-02601-1
Saegyeol Jung, Byeongjun Seok, Chang jae Roh, Younsik Kim, Donghan Kim, Yeonjae Lee, San Kang, Shigeyuki Ishida, Shik Shin, Hiroshi Eisaki, Tae Won Noh, Dongjoon Song, Changyoung Kim
Identifying ordered phases and their underlying symmetries in materials that exhibit high-temperature superconductivity is an important step towards understanding the mechanism of that phenomenon. Indeed, the critical behaviour related to phase transitions of those ordered phases is expected to be correlated with the superconductivity. In cuprate materials, efforts to find such ordered phases have mainly focused on symmetry breaking in the pseudogap region whereas the Fermi-liquid-like metallic region beyond the so-called critical doping at which the pseudogap disappears has been regarded as a trivial disordered state. Here, we uncover a broken mirror symmetry in the Fermi-liquid-like phase in (Bi,Pb)2Sr2CaCu2O8+δ beyond the critical doping. We do this by tracking the temperature dependence of the rotational-anisotropy of second-harmonic generation for two different dopings. We observe behaviour reminiscent of an order parameter with an onset temperature that coincides with the strange metal to Fermi-liquid-like metal crossover. Angle-resolved photoemission spectroscopy shows that the quasiparticle coherence between CuO2 bilayers is enhanced in proportion to the symmetry-breaking response as a function of temperature, suggesting that the change in metallicity and symmetry breaking are linked. These observations contradict the conventional quantum disordered scenario for over-critical-doped cuprates. The Fermi liquid state in highly doped superconducting cuprates is normally thought of as disordered. Now, an observation of broken mirror symmetry in that phase suggests otherwise.
{"title":"Spontaneous breaking of mirror symmetry in a cuprate beyond critical doping","authors":"Saegyeol Jung, Byeongjun Seok, Chang jae Roh, Younsik Kim, Donghan Kim, Yeonjae Lee, San Kang, Shigeyuki Ishida, Shik Shin, Hiroshi Eisaki, Tae Won Noh, Dongjoon Song, Changyoung Kim","doi":"10.1038/s41567-024-02601-1","DOIUrl":"10.1038/s41567-024-02601-1","url":null,"abstract":"Identifying ordered phases and their underlying symmetries in materials that exhibit high-temperature superconductivity is an important step towards understanding the mechanism of that phenomenon. Indeed, the critical behaviour related to phase transitions of those ordered phases is expected to be correlated with the superconductivity. In cuprate materials, efforts to find such ordered phases have mainly focused on symmetry breaking in the pseudogap region whereas the Fermi-liquid-like metallic region beyond the so-called critical doping at which the pseudogap disappears has been regarded as a trivial disordered state. Here, we uncover a broken mirror symmetry in the Fermi-liquid-like phase in (Bi,Pb)2Sr2CaCu2O8+δ beyond the critical doping. We do this by tracking the temperature dependence of the rotational-anisotropy of second-harmonic generation for two different dopings. We observe behaviour reminiscent of an order parameter with an onset temperature that coincides with the strange metal to Fermi-liquid-like metal crossover. Angle-resolved photoemission spectroscopy shows that the quasiparticle coherence between CuO2 bilayers is enhanced in proportion to the symmetry-breaking response as a function of temperature, suggesting that the change in metallicity and symmetry breaking are linked. These observations contradict the conventional quantum disordered scenario for over-critical-doped cuprates. The Fermi liquid state in highly doped superconducting cuprates is normally thought of as disordered. Now, an observation of broken mirror symmetry in that phase suggests otherwise.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 10","pages":"1616-1621"},"PeriodicalIF":17.6,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141877403","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-02DOI: 10.1038/s41567-024-02602-0
Alessandra Milloch, Claudio Giannetti
A new ferroic-like phase has been discovered in highly doped superconducting cuprates. The existence of a well-defined order parameter on the supposedly disordered side of the phase diagram challenges the accepted theoretical framework.
{"title":"New order in the copper oxide phase diagram","authors":"Alessandra Milloch, Claudio Giannetti","doi":"10.1038/s41567-024-02602-0","DOIUrl":"10.1038/s41567-024-02602-0","url":null,"abstract":"A new ferroic-like phase has been discovered in highly doped superconducting cuprates. The existence of a well-defined order parameter on the supposedly disordered side of the phase diagram challenges the accepted theoretical framework.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 10","pages":"1527-1528"},"PeriodicalIF":17.6,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141877568","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-01DOI: 10.1038/s41567-024-02584-z
Ranyiliu Chen, Laura Mančinska, Jurij Volčič
Entangled quantum systems feature non-local correlations that are stronger than could be realized classically. This property makes it possible to perform self-testing, the strongest form of quantum functionality verification, which allows a classical user to deduce the quantum state and measurements used to produce a given set of measurement statistics. While self-testing of quantum states is well understood, self-testing of measurements, especially in high dimensions, remains relatively unexplored. Here we prove that every real projective measurement can be self-tested. Our approach employs the idea that existing self-tests can be extended to verify additional untrusted measurements, known as post-hoc self-testing. We formalize the method of post-hoc self-testing and establish the condition under which it can be applied. Using this condition, we construct self-tests for all real projective measurements. We build on this result to develop an iterative self-testing technique that provides a clear methodology for constructing new self-tests from pre-existing ones. Quantum correlations are strong enough that classical users can verify that a device produces quantum entangled states using only the outcomes of local measurements. This self-testing approach has now been extended to verifying quantum measurements.
{"title":"All real projective measurements can be self-tested","authors":"Ranyiliu Chen, Laura Mančinska, Jurij Volčič","doi":"10.1038/s41567-024-02584-z","DOIUrl":"10.1038/s41567-024-02584-z","url":null,"abstract":"Entangled quantum systems feature non-local correlations that are stronger than could be realized classically. This property makes it possible to perform self-testing, the strongest form of quantum functionality verification, which allows a classical user to deduce the quantum state and measurements used to produce a given set of measurement statistics. While self-testing of quantum states is well understood, self-testing of measurements, especially in high dimensions, remains relatively unexplored. Here we prove that every real projective measurement can be self-tested. Our approach employs the idea that existing self-tests can be extended to verify additional untrusted measurements, known as post-hoc self-testing. We formalize the method of post-hoc self-testing and establish the condition under which it can be applied. Using this condition, we construct self-tests for all real projective measurements. We build on this result to develop an iterative self-testing technique that provides a clear methodology for constructing new self-tests from pre-existing ones. Quantum correlations are strong enough that classical users can verify that a device produces quantum entangled states using only the outcomes of local measurements. This self-testing approach has now been extended to verifying quantum measurements.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 10","pages":"1642-1647"},"PeriodicalIF":17.6,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41567-024-02584-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141877405","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-29DOI: 10.1038/s41567-024-02563-4
Spin-squeezed states are a resource for quantum-enhanced precision measurement. However, the theoretical foundations for scalable spin squeezing — where quantum enhancement grows with system size — have only been established for systems exhibiting all-to-all interactions. Now, by unveiling a connection to finite-temperature magnetism, scalable squeezing is extended to locally interacting systems.
{"title":"Scalable spin squeezing with local interactions","authors":"","doi":"10.1038/s41567-024-02563-4","DOIUrl":"10.1038/s41567-024-02563-4","url":null,"abstract":"Spin-squeezed states are a resource for quantum-enhanced precision measurement. However, the theoretical foundations for scalable spin squeezing — where quantum enhancement grows with system size — have only been established for systems exhibiting all-to-all interactions. Now, by unveiling a connection to finite-temperature magnetism, scalable squeezing is extended to locally interacting systems.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 10","pages":"1538-1539"},"PeriodicalIF":17.6,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141791068","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-29DOI: 10.1038/s41567-024-02592-z
Kyuhwan Lee, Sol Kim, Taehoon Kim, Y. Shin
The Kibble–Zurek mechanism is a theoretical framework that describes the formation and scaling of topological defects in symmetry-breaking phase transitions. It was originally conceptualized for superfluid helium. The theory predicts that the number of quantum vortices should scale as a power law with the rate at which the system passes through the lambda transition, but demonstrating this effect has been elusive in experiments using superfluid systems. Here, we report the observation of Kibble–Zurek scaling in a homogeneous, strongly interacting Fermi gas undergoing a superfluid phase transition. We investigate the superfluid transition using temperature and interaction strength as two distinct control parameters. The microscopic physics of condensate formation is markedly different for the two quench parameters, as shown by the two orders of magnitude difference in the condensate formation timescale. However, regardless of the thermodynamic direction in which the system passes through a phase transition, the Kibble–Zurek exponent is identically observed to be about 0.68, in good agreement with theoretical predictions. This work experimentally demonstrates the theoretical proposal laid out for liquid helium, which is in the same universality class as strongly interacting Fermi gases. An experiment proves that strongly interacting Fermi gases driven into a superfluid phase by two different quenches display the same universal dynamics in the framework of the Kibble–Zurek mechanism.
{"title":"Universal Kibble–Zurek scaling in an atomic Fermi superfluid","authors":"Kyuhwan Lee, Sol Kim, Taehoon Kim, Y. Shin","doi":"10.1038/s41567-024-02592-z","DOIUrl":"10.1038/s41567-024-02592-z","url":null,"abstract":"The Kibble–Zurek mechanism is a theoretical framework that describes the formation and scaling of topological defects in symmetry-breaking phase transitions. It was originally conceptualized for superfluid helium. The theory predicts that the number of quantum vortices should scale as a power law with the rate at which the system passes through the lambda transition, but demonstrating this effect has been elusive in experiments using superfluid systems. Here, we report the observation of Kibble–Zurek scaling in a homogeneous, strongly interacting Fermi gas undergoing a superfluid phase transition. We investigate the superfluid transition using temperature and interaction strength as two distinct control parameters. The microscopic physics of condensate formation is markedly different for the two quench parameters, as shown by the two orders of magnitude difference in the condensate formation timescale. However, regardless of the thermodynamic direction in which the system passes through a phase transition, the Kibble–Zurek exponent is identically observed to be about 0.68, in good agreement with theoretical predictions. This work experimentally demonstrates the theoretical proposal laid out for liquid helium, which is in the same universality class as strongly interacting Fermi gases. An experiment proves that strongly interacting Fermi gases driven into a superfluid phase by two different quenches display the same universal dynamics in the framework of the Kibble–Zurek mechanism.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 10","pages":"1570-1574"},"PeriodicalIF":17.6,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141790981","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-29DOI: 10.1038/s41567-024-02582-1
Yuan Zhan, Shuo Sun
Creating entangled photon pairs often requires intense excitation of nonlinear materials or the active manipulation of quantum devices. Now, entanglement between two photons has been created by scattering a laser off a passive quantum dot.
{"title":"A single quantum dot passively mediates entanglement","authors":"Yuan Zhan, Shuo Sun","doi":"10.1038/s41567-024-02582-1","DOIUrl":"10.1038/s41567-024-02582-1","url":null,"abstract":"Creating entangled photon pairs often requires intense excitation of nonlinear materials or the active manipulation of quantum devices. Now, entanglement between two photons has been created by scattering a laser off a passive quantum dot.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 9","pages":"1363-1364"},"PeriodicalIF":17.6,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141791069","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-29DOI: 10.1038/s41567-024-02599-6
A quantum control technique is used to directly couple trapped-ion motional modes with high fidelity, enabling non-destructive measurements of the quantum harmonic oscillator states of atomic motion. The strong coupling rate and precise manipulation of the quantum states achieved with this technique could lead to advances in quantum information processing.
{"title":"Precise control and non-destructive readout of quantum states of ion motion","authors":"","doi":"10.1038/s41567-024-02599-6","DOIUrl":"10.1038/s41567-024-02599-6","url":null,"abstract":"A quantum control technique is used to directly couple trapped-ion motional modes with high fidelity, enabling non-destructive measurements of the quantum harmonic oscillator states of atomic motion. The strong coupling rate and precise manipulation of the quantum states achieved with this technique could lead to advances in quantum information processing.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 10","pages":"1544-1545"},"PeriodicalIF":17.6,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141791070","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-29DOI: 10.1038/s41567-024-02562-5
Maxwell Block, Bingtian Ye, Brenden Roberts, Sabrina Chern, Weijie Wu, Zilin Wang, Lode Pollet, Emily J. Davis, Bertrand I. Halperin, Norman Y. Yao
Spin squeezing is a form of entanglement that reshapes the quantum projection noise to improve measurement precision. Here, we provide numerical and analytic evidence for the following conjecture: any Hamiltonian exhibiting finite-temperature easy-plane ferromagnetism can be used to generate scalable spin squeezing, thereby enabling quantum-enhanced sensing. Our conjecture is guided by a connection between the quantum Fisher information of pure states and the spontaneous breaking of a continuous symmetry. We demonstrate that spin squeezing exhibits a phase diagram with a sharp transition between scalable squeezing and non-squeezing. This transition coincides with the equilibrium phase boundary for XY order at a finite temperature. In the scalable squeezing phase, we predict a sensitivity scaling that lies between the standard quantum limit and the scaling achieved in all-to-all coupled one-axis twisting models. A corollary of our conjecture is that short-ranged versions of two-axis twisting cannot yield scalable metrological gain. Our results provide insights into the landscape of Hamiltonians that can be used to generate metrologically useful quantum states. Generating highly squeezed states for quantum sensing requires precise entanglement properties, which makes it a hard task. Now a conjecture identifies a realistic regime of magnetic order at finite temperatures that enables scalable spin squeezing.
{"title":"Scalable spin squeezing from finite-temperature easy-plane magnetism","authors":"Maxwell Block, Bingtian Ye, Brenden Roberts, Sabrina Chern, Weijie Wu, Zilin Wang, Lode Pollet, Emily J. Davis, Bertrand I. Halperin, Norman Y. Yao","doi":"10.1038/s41567-024-02562-5","DOIUrl":"10.1038/s41567-024-02562-5","url":null,"abstract":"Spin squeezing is a form of entanglement that reshapes the quantum projection noise to improve measurement precision. Here, we provide numerical and analytic evidence for the following conjecture: any Hamiltonian exhibiting finite-temperature easy-plane ferromagnetism can be used to generate scalable spin squeezing, thereby enabling quantum-enhanced sensing. Our conjecture is guided by a connection between the quantum Fisher information of pure states and the spontaneous breaking of a continuous symmetry. We demonstrate that spin squeezing exhibits a phase diagram with a sharp transition between scalable squeezing and non-squeezing. This transition coincides with the equilibrium phase boundary for XY order at a finite temperature. In the scalable squeezing phase, we predict a sensitivity scaling that lies between the standard quantum limit and the scaling achieved in all-to-all coupled one-axis twisting models. A corollary of our conjecture is that short-ranged versions of two-axis twisting cannot yield scalable metrological gain. Our results provide insights into the landscape of Hamiltonians that can be used to generate metrologically useful quantum states. Generating highly squeezed states for quantum sensing requires precise entanglement properties, which makes it a hard task. Now a conjecture identifies a realistic regime of magnetic order at finite temperatures that enables scalable spin squeezing.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 10","pages":"1575-1581"},"PeriodicalIF":17.6,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141791071","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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